2,420 research outputs found
Andreev scattering in nanoscopic junctions at high magnetic fields
We report on the measurement of multiple Andreev resonances at atomic size
point contacts between two superconducting nanostructures of Pb under magnetic
fields higher than the bulk critical field, where superconductivity is
restricted to a mesoscopic region near the contact. The small number of
conduction channels in this type of contacts permits a quantitative comparison
with theory through the whole field range. We discuss in detail the physical
properties of our structure, in which the normal bulk electrodes induce a
proximity effect into the mesoscopic superconducting part.Comment: 4 page
Radiation of a relativistic electron with non-equilibrium own Coulomb field
The condition and specific features of the non-dipole regime of radiation is discussed in the context of the results of the recent CERN experiment NA63 on measurement of the radiation power spectrum of 149 GeV electrons in thin
tantalum targets. The first observation of a logarithmic dependence of radiation yield on the target thickness that was done there is the conclusive evidence of the effect of radiation suppression in a thin layer of matter, which was predicted many years ago, and which is the direct manifestation of the radiation of a relativistic electron with non-equilibrium own Coulomb field. The special features of the angular distribution of the radiation and its polarization in a thin target at non-dipole regime are proposed for a new experimental study
Generating Scientifically Proven Knowledge about Ontology of Open Systems. Multidimensional Knowledge-Centric System Analytics
Physics of open systems overcomes real complexity of open systems, perceives them in natural scale without resorting to expert knowledge, subjective analysis and interpretations. Its scientific methods and technologies produce scientifically proven ontological knowledge from the systems’ empirical descriptions that in turn are gathered from a huge amount of semi-structured, multimodal, multidimensional, and heterogeneous data, provide scientific understanding and rational explanation of obtained knowledge, research its value (correctness, fullness, and completeness), and carry out a deep and detailed analytics of multidimensional open systems on the basis of knowledge about their ontology
Space-time in light of Karolyhazy uncertainty relation
General relativity and quantum mechanics provide a natural explanation for
the existence of dark energy with its observed value and predict its dynamics.
Dark energy proves to be necessary for the existence of space-time itself and
determines the rate of its stability.Comment: 5 pages, Two misprints are correcte
Characteristic Potentials for Mesoscopic Rings Threaded by an Aharonov-Bohm Flux
Electro-static potentials for samples with the topology of a ring and
penetrated by an Aharonov-Bohm flux are discussed. The sensitivity of the
electron-density distribution to small variations in the flux generates an
effective electro-static potential which is itself a periodic function of flux.
We investigate a simple model in which the flux sensitive potential leads to a
persistent current which is enhanced compared to that of a loop of
non-interacting electrons. For sample geometries with contacts the sensitivity
of the electro-static potential to flux leads to a flux-induced capacitance.
This capacitance gives the variation in charge due to an increment in flux. The
flux-induced capacitance is contrasted with the electro-chemical capacitance
which gives the variation in charge due to an increment in an electro-chemical
potential. The discussion is formulated in terms of characteristic functions
which give the variation of the electro-static potential in the interior of the
conductor due to an increment in the external control parameters (flux,
electro-chemical potentials). Paper submitted to the 16th Nordic Semiconductor
Meeting, Laugarvatan, Iceland, June 12-15, 1994. The proceedings will be
published in Physica Scripta.Comment: 23 pages + 4 figures, revtex, IBM-RC1955
Time-inconsistent Planning: Simple Motivation Is Hard to Find
With the introduction of the graph-theoretic time-inconsistent planning model
due to Kleinberg and Oren, it has been possible to investigate the
computational complexity of how a task designer best can support a
present-biased agent in completing the task. In this paper, we study the
complexity of finding a choice reduction for the agent; that is, how to remove
edges and vertices from the task graph such that a present-biased agent will
remain motivated to reach his target even for a limited reward. While this
problem is NP-complete in general, this is not necessarily true for instances
which occur in practice, or for solutions which are of interest to task
designers. For instance, a task designer may desire to find the best task graph
which is not too complicated.
We therefore investigate the problem of finding simple motivating subgraphs.
These are structures where the agent will modify his plan at most times
along the way. We quantify this simplicity in the time-inconsistency model as a
structural parameter: The number of branching vertices (vertices with
out-degree at least ) in a minimal motivating subgraph.
Our results are as follows: We give a linear algorithm for finding an optimal
motivating path, i.e. when . On the negative side, we show that finding a
simple motivating subgraph is NP-complete even if we allow only a single
branching vertex --- revealing that simple motivating subgraphs are indeed hard
to find. However, we give a pseudo-polynomial algorithm for the case when
is fixed and edge weights are rationals, which might be a reasonable assumption
in practice.Comment: An extended abstract of this paper is accepted at AAAI 202
Efficient Exact Algorithms on Planar Graphs: Exploiting Sphere Cut Decompositions
A divide-and-conquer strategy based on variations of the Lipton-Tarjan planar separator
theorem has been one of the most common approaches for solving planar graph problems for
more than 20 years. We present a new framework for designing fast subexponential exact and parameterized algorithms on planar graphs. Our approach is based on geometric properties of planar branch decompositions obtained by Seymour & Thomas, combined with refined techniques of dynamic programming on planar graphs based on properties of non-crossing partitions. Compared to divide-and-conquer algorithms, the main advantages of our method are a) it is a generic method which allows to attack broad classes of problems; b) the obtained algorithms provide a better worst case analysis. To exemplify our approach we show how to obtain an O(26.903√n) time algorithm solving weighted HAMILTONIAN CYCLE. We observe how our technique can be used to solve PLANAR GRAPH TSP in time O(29.8594√n). Our approach can be used to design parameterized algorithms as well. For example we introduce the first 2O(√ k)nO(1) time algorithm for parameterized Planar k-cycle by showing that for a given k we can decide if a planar graph on n vertices has a cycle of length at least k in time O(213.6√kn + n3)
(Total) Vector Domination for Graphs with Bounded Branchwidth
Given a graph of order and an -dimensional non-negative
vector , called demand vector, the vector domination
(resp., total vector domination) is the problem of finding a minimum
such that every vertex in (resp., in ) has
at least neighbors in . The (total) vector domination is a
generalization of many dominating set type problems, e.g., the dominating set
problem, the -tuple dominating set problem (this is different from the
solution size), and so on, and its approximability and inapproximability have
been studied under this general framework. In this paper, we show that a
(total) vector domination of graphs with bounded branchwidth can be solved in
polynomial time. This implies that the problem is polynomially solvable also
for graphs with bounded treewidth. Consequently, the (total) vector domination
problem for a planar graph is subexponential fixed-parameter tractable with
respectto , where is the size of solution.Comment: 16 page
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