2,029 research outputs found
Phase diagram and dynamic response functions of the Holstein-Hubbard model
We present the phase diagram and dynamical correlation functions for the
Holstein-Hubbard model at half filling and at zero temperature. The
calculations are based on the Dynamical Mean Field Theory. The effective
impurity model is solved using Exact Diagonalization and the Numerical
Renormalization Group. Excluding long-range order, we find three different
paramagnetic phases, metallic, bipolaronic and Mott insulating, depending on
the Hubbard interaction U and the electron-phonon coupling g. We present the
behaviour of the one-electron spectral functions and phonon spectra close to
the metal insulator transitions.Comment: contribution to the SCES04 conferenc
First- and Second Order Phase Transitions in the Holstein-Hubbard Model
We investigate metal-insulator transitions in the Holstein-Hubbard model as a
function of the on-site electron-electron interaction U and the electron-phonon
coupling g. We use several different numerical methods to calculate the phase
diagram, the results of which are in excellent agreement. When the
electron-electron interaction U is dominant the transition is to a
Mott-insulator; when the electron-phonon interaction dominates, the transition
is to a localised bipolaronic state. In the former case, the transition is
always found to be second order. This is in contrast to the transition to the
bipolaronic state, which is clearly first order for larger values of U. We also
present results for the quasiparticle weight and the double-occupancy as
function of U and g.Comment: 6 pages, 5 figure
Polaronic signature in the metallic phase of La0.7Ca0.3MnO3 films detected by scanning tunneling spectroscopy
In this work we map tunnel conductance curves with nanometric spatial
resolution, tracking polaronic quasiparticle excitations when cooling across
the insulator-to-metal transition in La0.7Ca0.3MnO3 films. In the insulating
phase the spectral signature of polarons, a depletion of conductance at low
bias flanked by peaks, is detected all over the scanned surface. These features
are still observed at the transition and persist on cooling into the metallic
phase. Polaron-binding energy maps reveal that polarons are not confined to
regions embedded in a highly-conducting matrix but are present over the whole
field of view both above and below the transition temperature.Comment: 10 pages, 4 figure
Major basic protein, but not eosinophil cationic protein or eosinophil protein X, is related to atopy in cystic fibrosis.
Increased eosinophil granule proteins have been described in serum and sputum samples of patients with cystic fibrosis (CF). It has been assumed that eosinophil degranulation is enhanced in atopic subjects - as in asthmatics. Since in CF no differences in eosinophil cationic protein (ECP), eosinophil protein X (EPX), and eosinophil peroxidase between atopic and nonatopic subjects have been detected, we investigated whether major basic protein (MBP) is increased in serum and sputum samples derived from atopic (n = 14) compared with nonatopic CF subjects (n = 26). In CF patients, high mean serum (sputum) levels of ECP 29.7 microg/l (2.7 mg/l), EPX 53.7 microg/l (7.9 mg/l), and MBP 984.6 microg/l but low sputum MBP levels (57.4 microg/l) were measured. In addition, in serum and in sputum samples, a significant correlation between MBP and ECP (P<0.03 and P<0.0001, respectively) or EPX (P<0.05 and P<0.0004, respectively) was detected. By subdivision of the patients into allergic and nonallergic subjects, significant differences were found for serum MBP values only(mean 1382.2 microg/l vs. 770.5 microg/l; P<0.0001), but not for ECP or EPX serum levels or for eosinophil proteins in sputum. Although no differences between atopic and nonatopic CF patients in ECP and EPX were found, serum MBP levels were higher in patients sensitized to inhalant allergens than in nonsensitized subjects. These results indicate differential release of eosinophil granule proteins in peripheral blood from eosinophils, and they also indicate that MBP in serum likely is to be a better discriminator of atopy in CF
Hard Occlusions in Visual Object Tracking
Visual object tracking is among the hardest problems in computer vision, as
trackers have to deal with many challenging circumstances such as illumination
changes, fast motion, occlusion, among others. A tracker is assessed to be good
or not based on its performance on the recent tracking datasets, e.g., VOT2019,
and LaSOT. We argue that while the recent datasets contain large sets of
annotated videos that to some extent provide a large bandwidth for training
data, the hard scenarios such as occlusion and in-plane rotation are still
underrepresented. For trackers to be brought closer to the real-world scenarios
and deployed in safety-critical devices, even the rarest hard scenarios must be
properly addressed. In this paper, we particularly focus on hard occlusion
cases and benchmark the performance of recent state-of-the-art trackers (SOTA)
on them. We created a small-scale dataset containing different categories
within hard occlusions, on which the selected trackers are evaluated. Results
show that hard occlusions remain a very challenging problem for SOTA trackers.
Furthermore, it is observed that tracker performance varies wildly between
different categories of hard occlusions, where a top-performing tracker on one
category performs significantly worse on a different category. The varying
nature of tracker performance based on specific categories suggests that the
common tracker rankings using averaged single performance scores are not
adequate to gauge tracker performance in real-world scenarios.Comment: Accepted at ECCV 2020 Workshop RLQ-TO
Contextual Object Detection with a Few Relevant Neighbors
A natural way to improve the detection of objects is to consider the
contextual constraints imposed by the detection of additional objects in a
given scene. In this work, we exploit the spatial relations between objects in
order to improve detection capacity, as well as analyze various properties of
the contextual object detection problem. To precisely calculate context-based
probabilities of objects, we developed a model that examines the interactions
between objects in an exact probabilistic setting, in contrast to previous
methods that typically utilize approximations based on pairwise interactions.
Such a scheme is facilitated by the realistic assumption that the existence of
an object in any given location is influenced by only few informative locations
in space. Based on this assumption, we suggest a method for identifying these
relevant locations and integrating them into a mostly exact calculation of
probability based on their raw detector responses. This scheme is shown to
improve detection results and provides unique insights about the process of
contextual inference for object detection. We show that it is generally
difficult to learn that a particular object reduces the probability of another,
and that in cases when the context and detector strongly disagree this learning
becomes virtually impossible for the purposes of improving the results of an
object detector. Finally, we demonstrate improved detection results through use
of our approach as applied to the PASCAL VOC and COCO datasets
Bayesian Network Structure Learning with Permutation Tests
In literature there are several studies on the performance of Bayesian
network structure learning algorithms. The focus of these studies is almost
always the heuristics the learning algorithms are based on, i.e. the
maximisation algorithms (in score-based algorithms) or the techniques for
learning the dependencies of each variable (in constraint-based algorithms). In
this paper we investigate how the use of permutation tests instead of
parametric ones affects the performance of Bayesian network structure learning
from discrete data. Shrinkage tests are also covered to provide a broad
overview of the techniques developed in current literature.Comment: 13 pages, 4 figures. Presented at the Conference 'Statistics for
Complex Problems', Padova, June 15, 201
WR-1.5 (500–750 GHz) waveguide bandpass filter fabricated using high precision computer numerically controlled machining
In this paper, a WR-1.5 band (500–750 GHz) 3rd order waveguide bandpass filter has been designed and fabricated using high precision computer numerically controlled metal micromachining. The filter has been measured with a 7.29% (48.7 GHz) bandwidth at the center frequency of 667.5 GHz. The minimum passband insertion loss is measured to be 0.87 dB and the measured return loss is better than 10 dB across the whole passband. A yield percentage is analysed and estimated based on the fabrication tolerance.</p
- …