9,546 research outputs found
Zero-mode contribution to the light-front Hamiltonian of Yukawa type models
Light-front Hamiltonian for Yukawa type models is determined without the
framework of canonical light-front formalism. Special attention is given to the
contribution of zero modes.Comment: 14 pages, Latex, revised version with minor changes, Submitted to
J.Phys.
Canonical formulation of the embedded theory of gravity equivalent to Einstein's General Relativity
We study the approach in which independent variables describing gravity are
functions of the space-time embedding into a flat space of higher dimension. We
formulate a canonical formalism for such a theory in a form, which requires
imposing additional constraints, which are a part of Einstein's equations. As a
result, we obtain a theory with an eight-parameter gauge symmetry. This theory
becomes equivalent to Einstein's general relativity either after partial gauge
fixing or after rewriting the metric in the form that is invariant under the
additional gauge transformations. We write the action for such a theory.Comment: LaTeX, 17 page
Theory and simulation of the dynamics, deformation, and breakup of a chain of superparamagnetic beads under a rotating magnetic field
In this work, an analytical model for the behavior of superparamagnetic chains under the effect of a rotating magnetic field is presented. It is postulated that the relevant mechanisms for describing the shape and breakup of the chains into smaller fragments are the induced dipole-dipole magnetic force on the external beads, their translational and rotational drag forces, and the tangential lubrication between particles. Under this assumption, the characteristic S-shape of the chain can be qualitatively understood. Furthermore, based on a straight chain approximation, a novel analytical expression for the critical frequency for the chain breakup is obtained. In order to validate the model, the analytical expressions are compared with full three-dimensional smoothed particle hydrodynamics simulations of magnetic beads showing excellent agreement. Comparison with previous theoretical results and experimental data is also reported
Mid-term report for the CORE Organic II funded project. “Innovative cropping Practices to increase soil health of organic fruit tree orchards” BIO-INCROP
Activities performed in the first part of BIO-INCROP project concern five of the eight main objectives fixed in the project proposal. They are:
Evaluation of soil borne pest and pathogens involved in replant disease
Role of rhizospheric bacterial and fungal communities in plant health
Selection of naturally available resources to increase microbial diversity and biomass
Compost and organic amendments
Evaluation of biologically active formulates
The document reports main research results and shows main items of dissemination activity performed in the first part of the project
Large-uncertainty intelligent states for angular momentum and angle
The equality in the uncertainty principle for linear momentum and position is
obtained for states which also minimize the uncertainty product. However, in
the uncertainty relation for angular momentum and angular position both sides
of the inequality are state dependent and therefore the intelligent states,
which satisfy the equality, do not necessarily give a minimum for the
uncertainty product. In this paper, we highlight the difference between
intelligent states and minimum uncertainty states by investigating a class of
intelligent states which obey the equality in the angular uncertainty relation
while having an arbitrarily large uncertainty product. To develop an
understanding for the uncertainties of angle and angular momentum for the
large-uncertainty intelligent states we compare exact solutions with analytical
approximations in two limiting cases.Comment: 20 pages, 9 figures, submitted to J. Opt. B special issue in
connection with ICSSUR 2005 conferenc
Resonant electron heating and molecular phonon cooling in single C junctions
We study heating and heat dissipation of a single \c60 molecule in the
junction of a scanning tunneling microscope (STM) by measuring the electron
current required to thermally decompose the fullerene cage. The power for
decomposition varies with electron energy and reflects the molecular resonance
structure. When the STM tip contacts the fullerene the molecule can sustain
much larger currents. Transport simulations explain these effects by molecular
heating due to resonant electron-phonon coupling and molecular cooling by
vibrational decay into the tip upon contact formation.Comment: Accepted in Phys. Rev. Let
Evidence for magnetic clusters in NiV close to the quantum critical concentration
The d-metal alloy NiV undergoes a quantum phase transition from
a ferromagnetic ground state to a paramagnetic ground state as the vanadium
concentration is increased. We present magnetization, ac-susceptibility and
muon-spin relaxation data at several vanadium concentrations near the critical
concentration at which the onset of ferromagnetic order is
suppressed to zero temperature. Below , the muon data reveal a broad
magnetic field distribution indicative of long-range ordered ferromagnetic
state with spatial disorder. We show evidence of magnetic clusters in the
ferromagnetic phase and close to the phase boundary in this disordered
itinerant system as an important generic ingredient of a disordered quantum
phase transition. In contrast, the temperature dependence of the magnetic
susceptibility above is best described in terms of a magnetic quantum
Griffiths phase with a power-law distribution of fluctuation rates of dynamic
magnetic clusters. At the lowest temperatures, the onset of a short-range
ordered cluster-glass phase is recognized by an increase in the muon
depolarization in transverse fields and maxima in ac-susceptibility.Comment: 6 pages, 5 figures, submitted to Proceedings of SCES 201
Lifelong learning in evolving graphs with limited labeled data and unseen class detection
Large-scale graph data in the real-world are often dynamic rather than static. The data are changing with new nodes, edges, and even classes appearing over time, such as in citation networks and research-and-development collaboration networks. Graph neural networks (GNNs) have emerged as the standard method for numerous tasks on graph-structured data. In this work, we employ a two-step procedure to explore how GNNs can be incrementally adapted to new unseen graph data. First, we analyze the verge between transductive and inductive learning on standard benchmark datasets. After inductive pretraining, we add unlabeled data to the graph and show that the models are stable. Then, we explore the case of continually adding more and more labeled data, while considering cases, where not all past instances are annotated with class labels. Furthermore, we introduce new classes while the graph evolves and explore methods that automatically detect instances from previously unseen classes. In order to deal with evolving graphs in a principled way, we propose a lifelong learning framework for graph data along with an evaluation protocol. In this framework, we evaluate representative GNN architectures. We observe that implicit knowledge within model parameters becomes more important when explicit knowledge, i.e., data from past tasks, is limited. We find that in open-world node classification, the data from surprisingly few past tasks are sufficient to reach the performance reached by remembering data from all past tasks. In the challenging task of unseen class detection, we find that using a weighted cross-entropy loss is important for stabilit
Constraint algebra for Regge-Teitelboim formulation of gravity
We consider the formulation of the gravity theory first suggested by Regge
and Teitelboim where the space-time is a four-dimensional surface in a flat
ten-dimensional space. We investigate a canonical formalism for this theory
following the approach suggested by Regge and Teitelboim. Under constructing
the canonical formalism we impose additional constraints agreed with the
equations of motion. We obtain the exact form of the first-class constraint
algebra. We show that this algebra contains four constraints which form a
subalgebra (the ideal), and if these constraints are fulfilled, the algebra
becomes the constraint algebra of the Arnowitt-Deser-Misner formalism of
Einstein's gravity. The reasons for the existence of additional first-class
constraints in the canonical formalism are discussed.Comment: LaTeX, 12 pages; in this version the misprints in eq. (37) and (41)
was correcte
ArUcoE: Enhanced ArUco Marker
This paper presents a novel fiducial marker type called ArUcoE. It is obtained from a standard ArUco marker by enhancing it with a chessboard-like pattern. With our approach the pose estimation accuracy of any ArUco marker can easily be increased. Further methods to increase the accuracy are analyzed. By applying a subpixel algorithm to the corner regions we are able to locate the corner points within a pixel and overcome the restriction of pixel-level accuracy. A deep-learning-based super-resolution method is used to artificially increase the pixel density in the same regions. Additionally, the effect of using a single and a stereo camera setup on the accuracy is shown
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