8,753 research outputs found
Nanoscale Impurity Structures on the Surface of -wave Superconductors
We study the effects of nanoscale impurity structures on the local electronic
structure of -wave superconductors. We show that the interplay
between the momentum dependence of the superconducting gap, the geometry of the
nanostructure and its orientation gives rise to a series of interesting quantum
effects. Among these are the emergence of a zero bias conductance peak in the
superconductor's density of states and the suppression of impurity states for
certain nanostructures. The latter effect can be used to screen impurity
resonances in the superconducting state.Comment: 4 pages, 5 figure
Particle and particle pair dispersion in turbulence modeled with spatially and temporally correlated stochastic processes
In this paper we present a new model for modeling the diffusion and relative
dispersion of particles in homogeneous isotropic turbulence. We use an
Heisenberg-like Hamiltonian to incorporate spatial correlations between fluid
particles, which are modeled by stochastic processes correlated in time. We are
able to reproduce the ballistic regime in the mean squared displacement of
single particles and the transition to a normal diffusion regime for long
times. For the dispersion of particle pairs we find a -dependence of the
mean squared separation at short times and a -dependence for long ones. For
intermediate times indications for a Richardson law are observed in
certain situations. Finally the influence of inertia of real particles on the
dispersion is investigated.Comment: 10 pages, 7 figures, 1 tabl
Focusing of opinions in the Deffuant model: First impression counts
The paper treats opinion dynamics of an unequal distribution as the initial
opinion distribution. Simulated is the Deffuant model on a directed
Barabasi-Albert network with discrete opinions and several subjects. Noticed is
a focusing of the the resulting opinion distribution during the simulation
towards the average value of the initial opinion distribution. A small change
of the focusing is seen. A dependency of this change on the number of subjects
and opinions is detected and indicates the change as a consequence of
discretization the opinions. Hereby the average value of the initial opinion
distribution can be identified as the guide of opinion forming.Comment: 8 pages including 5 figures, for Int. J. Mod. Phys.
Strong UV and X-ray variability of the Narrow Line Seyfert 1 Galaxy WPVS 007 -- on the nature of the X-ray low state
We report on multi-wavelength observations of the X-ray transient Narrow Line
Seyfert 1 (NLS1) galaxy WPVS 007. The galaxy was monitored with Swift between
October 2005 and July 2013, after it had undergone a dramatic drop in its X-ray
flux earlier. For the first time, we are able to repeatedly detect this NLS1 in
X-rays again. This increased number of detections in the last couple of years
may suggest that the strong absorber that has been found in this AGN is
starting to become leaky, and may eventually disappear. The X-ray spectra
obtained for WPVS 007 are all consistent with a partial covering absorber
model. A spectrum based on the data during the extreme low X-ray flux states
shows that the absorption column density is of the order of 4 x 10^23 cm^-2
with a covering fraction of 95%. WPVS 007 also displays one of the strongest UV
variabilities seen in Narrow Line Seyfert 1s. The UV continuum variability
anti-correlates with the optical/UV slope alpha-UV which suggests that the
variability primarily may be due to reddening. The UV variability time scales
are consistent with moving dust `clouds' located beyond the dust sublimation
radius of approximately 20 ld. We present for the first time near infrared JHK
data of WPVS 007, which reveal a rich emission-line spectrum. Recent optical
spectroscopy does not indicate significant variability in the broad and FeII
emission lines, implying that the ionizing continuum seen by those gas clouds
has not significantly changed over the last decades. All X-ray and UV
observations are consistent with a scenario in which an evolving Broad
Absorption Line (BAL) flow obscures the continuum emission. As such, WPVS 007
is an important target for our understanding of BAL flows in low-mass active
galactic nuclei (AGN).Comment: Accepted for publications in the Astronomical Journal; 29 pages, 10
Figures, 7 Table
Dissipationless Spin Current between Two Coupled Ferromagnets
We demonstrate the general principle which states that a dissipationless spin
current flows between two coupled ferromagnets if their magnetic orders are
misaligned. This principle applies regardless the two ferromagnets are metallic
or insulating, and also generally applies to bulk magnetic insulators. On a
phenomenological level, this principle is analogous to Josephson effect, and
yields a dissipationless spin current that is independent from scattering. The
microscopic mechanisms for the dissipationless spin current depend on the
systems, which are elaborated in details. A uniform, static magnetic field is
further proposed to be an efficient handle to create the misaligned
configuration and stabilize the dissipationless spin current.Comment: 10 pages, 5 figure
Realisation of Hardy's Thought Experiment
We present an experimental realisation of Hardy's thought experiment [Phys.
Rev. Lett. {\bf 68}, 2981 (1992)], using photons. The experiment consists of a
pair of Mach-Zehnder interferometers that interact through photon bunching at a
beam splitter. A striking contradiction is created between the predictions of
quantum mechanics and local hidden variable based theories. The contradiction
relies on non-maximally entangled position states of two particles.Comment: 5 page
Experimental investigation of quantum key distribution with position and momentum of photon pairs
We investigate the utility of Einstein-Podolsky-Rosen correlations of the
position and momentum of photon pairs from parametric down-conversion in the
implementation of a secure quantum key distribution protocol. We show that
security is guaranteed by the entanglement between downconverted pairs, and can
be checked by either direct comparison of Alice and Bob's measurement results
or evaluation of an inequality of the sort proposed by Mancini et al. (Phys.
Rev. Lett. 88, 120401 (2002)).Comment: 6 pages, 6 figures, subimitted for publicatio
Short-Timescale monitoring of the X-ray, UV and broad double-peak emission line of the nucleus of NGC 1097
Recent studies have suggested that the short-timescale ( days)
variability of the broad (10,000 km s) double-peaked H
profile of the LINER nucleus of NGC1097 could be driven by a variable X-ray
emission from a central radiatively inefficient accretion flow (RIAF). To test
this scenario, we have monitored the NGC1097 nucleus in X-ray and UV continuum
with Swift and the H flux and profile in the optical spectrum using
SOAR and Gemini-South from 2012 August to 2013 February. During the monitoring
campaign, the H flux remained at a very low level --- 3 times lower
than the maximum flux observed in previous campaigns and showing only limited
() variability. The X-ray variations were small, only
throughout the campaign, while the UV did not show significant variations. We
concluded that the timescale of the H profile variation is close to the
sampling interval of the optical observations, which results in only marginal
correlation between the X-ray and H fluxes. We have caught the AGN in
NGC1097 in a very low activity state, in which the ionizing source was very
weak and capable of ionizing just the innermost part of the gas in the disk.
Nonetheless, the data presented here still support the picture in which the gas
that emits the broad double-peaked Balmer lines is illuminated/ionized by a
source of high-energy photons which is located interior to the inner radius of
the line-emitting part of the disk.Comment: The paper contains 14 pages, 7 figures and is accepted for
publication at the Astrophysical Journa
- …