27,325 research outputs found
Quantum localized modes in capacitively coupled Josephson junctions
We consider the quantum dynamics of excitations in a system of two
capacitively coupled Josephson junctions. Quantum breather states are found in
the middle of the energy spectrum of the confined nonescaping states of the
system. They are characterized by a strong excitation of one junction. These
states perform slow tunneling motion from one junction to the other, while
keeping their coherent nature. The tunneling time sensitively depends on the
initial excitation energy. By using an external bias as a control parameter,
the tunneling time can be varied with respect to the escape time and the
experimentally limited coherence time. Thus one can control the flow of quantum
excitations between the two junctions.Comment: 5 pages, 3 figures. Improved version, title was slightly changed.
Accepted in Europhysics Letters (http://www.iop.org/EJ/journal/EPL
Quantum breathers in capacitively coupled Josephson junctions: Correlations, number conservation, and entanglement
We consider the classical and quantum dynamics of excitations in a system of
two capacitively coupled Josephson junctions. In the classical case the
equations of motion admit discrete breather solutions, which are time periodic
and localized predominantly on one of the junctions. In the quantum case
breather states are found in the central part of the energy spectrum of the
confined nonescaping states of the system. We perform a systematic analysis of
their tunneling frequency, site correlations, fluctuations of the number of
quanta, and entanglement. Quantum breather states show strong site correlation
of quanta and are characterized by a strong excitation of quanta on one
junction which perform slow coherent tunneling motion from one junction to the
other. They suppress fluctuations of the total number of excited quanta.
Quantum breather states are the least entangled states among the group of
eigenstates in the same range of the energy spectrum. We describe how quantum
breather excitations could be experimentally observed by employing the already
developed techniques for quantum information processing using Josephson
junctions.Comment: 10 pages, 9 figures. Improved version with further discussions.
Accepted in Physical Review
Coupling the solar surface and the corona: coronal rotation, Alfv\'en wave-driven polar plumes
The dynamical response of the solar corona to surface and sub-surface
perturbations depends on the chromospheric stratification, and specifically on
how efficiently these layers reflect or transmit incoming Alfv\'en waves. While
it would be desirable to include the chromospheric layers in the numerical
simulations used to study such phenomena, that is most often not feasible. We
defined and tested a simple approximation allowing the study of coronal
phenomena while taking into account a parametrised chromospheric reflectivity.
We addressed the problems of the transmission of the surface rotation to the
corona and that of the generation of polar plumes by Alfv\'en waves (Pinto et
al., 2010, 2011). We found that a high (yet partial) effective chromospheric
reflectivity is required to properly describe the angular momentum balance in
the corona and the way the surface differential rotation is transmitted
upwards. Alfv\'en wave-driven polar plumes maintain their properties for a wide
range of values for the reflectivity, but they become bursty (and eventually
disrupt) when the limit of total reflection is attained.Comment: Solar Wind 13: Proceedings of the Thirteenth International Solar Wind
Conferenc
Chronic hyponatremia in a patient with renal salt wasting and without cerebral disease: relationship between RSW, risk of fractures and cognitive impairment
Renal salt wasting syndrome (RSW) is defined as a renal loss of sodium leading to hyponatremia and a decrease in extracellular fluid volume (ECV). Differentiation of this disorder from the syndrome of inappropriate antidiuretic hormone secretion (SIADH), a common cause of hyponatremia, can be difficult because both can present with hyponatremia and concentrated urine with natriuresis. Our clinical case about a 78-year-old woman with a recent fracture of the right femur not only confirms that this syndrome can occur in patients without intracranial pathologies (CT documented), but depicts how the hyponatremia caused by RSW can show a chronic, oscillating course. This is an interesting point of view because it suggests to us to consider RSW in the differential diagnosis of patients with chronic hyponatremia
Flux-tube geometry and solar wind speed during an activity cycle
The solar wind speed at 1 AU shows variations in latitude and in time which
reflect the evolution of the global background magnetic field during the
activity cycle. It is commonly accepted that the terminal wind speed in a
magnetic flux-tube is anti-correlated with its expansion ratio, which motivated
the definition of widely-used semi-empirical scaling laws relating one to the
other. In practice, such scaling laws require ad-hoc corrections. A predictive
law based solely on physical principles is still missing. We test whether the
flux-tube expansion is the controlling factor of the wind speed at all phases
of the cycle and at all latitudes using a very large sample of wind-carrying
open magnetic flux-tubes. We furthermore search for additional physical
parameters based on the geometry of the coronal magnetic field which have an
influence on the terminal wind flow speed. We use MHD simulations of the corona
and wind coupled to a dynamo model to provide a large statistical ensemble of
open flux-tubes which we analyse conjointly in order to identify relations of
dependence between the wind speed and geometrical parameters of the flux-tubes
which are valid globally (for all latitudes and moments of the cycle). Our
study confirms that the terminal speed of the solar wind depends very strongly
on the geometry of the open magnetic flux-tubes through which it flows. The
total flux-tube expansion is more clearly anti-correlated with the wind speed
for fast rather than for slow wind flows, and effectively controls the
locations of these flows during solar minima. Overall, the actual asymptotic
wind speeds attained are also strongly dependent on field-line inclination and
magnetic field amplitude at the foot-points. We suggest ways of including these
parameters on future predictive scaling-laws for the solar wind speed.Comment: Accepted for publicaton on Astronomy & Astrophysic
Quantum q-breathers in a finite Bose-Hubbard chain: The case of two interacting bosons
We study the spectrum and eigenstates of the quantum discrete Bose-Hubbard
Hamiltonian in a finite one-dimensional lattice containing two bosons. The
interaction between the bosons leads to an algebraic localization of the
modified extended states in the normal mode space of the noninteracting system.
Weight functions of the eigenstates in the space of normal modes are computed
by using numerical diagonalization and perturbation theory. We find that
staggered states do not compactify in the dilute limit for large chains.Comment: 7 pages, 7 figures. Minor changes and additional comments. Acepted in
Physical Review
Quantum dynamics of localized excitations in a symmetric trimer molecule
We study the time evolution of localized (local bond) excitations in a
symmetric quantum trimer molecule. We relate the dynamical properties of
localized excitations such as their spectral intensity and their temporal
evolution (survival probability and tunneling of bosons) to their degree of
overlap with quantum tunneling pair states. We report on the existence of
degeneracy points in the trimer eigenvalue spectrum for specific values of
parameters due to avoided crossings between tunneling pair states and
additional states. The tunneling of localized excitations which overlap with
these degenerate states is suppressed on all times. As a result local bond
excitations may be strongly localized forever, similar to their classical
counterparts.Comment: 9 pages, 12 figures. Improved version with more discussions. Some
figures were replaced for better understanding. Accepted in Phys. Rev.
- …