92,647 research outputs found
On the threshold-width of graphs
The GG-width of a class of graphs GG is defined as follows. A graph G has
GG-width k if there are k independent sets N1,...,Nk in G such that G can be
embedded into a graph H in GG such that for every edge e in H which is not an
edge in G, there exists an i such that both endpoints of e are in Ni. For the
class TH of threshold graphs we show that TH-width is NP-complete and we
present fixed-parameter algorithms. We also show that for each k, graphs of
TH-width at most k are characterized by a finite collection of forbidden
induced subgraphs
Pickoff and spin-conversion quenchings of ortho-positronium in oxygen
The quenching processes of the thermalized ortho-positronium(o-Ps) on an
oxygen molecule have been studied by the positron annihilation age-momentum
correlation techinique(AMOC). The Doppler broadening spectrum of the 511 keV
gamma-rays from the 2gamma annihilation of o-Ps in O_2 has been measured as a
function of the o-Ps age. The rate of the quenching, consisting of the pickoff
and the spin-conversion, is estimated from the positron lifetime spectrum. The
ratio of the pickoff quenching rate to the spin-conversion rate is deduced from
the Doppler broadening of the 511 keV gamma-rays from the annihilation of the
o-Ps. The pickoff parameter ^1Z_eff, the effective number of the electrons per
molecule which contribute to the pickoff quenching, for O_2 is determined to be
0.6 +- 0.4. The cross-section for the elastic spin-conversion quenching is
determined to be (1.16 +- 0.01) * 10^{-19} cm^2.Comment: 4 pages with 5 eps figures, LaTeX2e(revtex4
Deep Learning Based Vehicle Make-Model Classification
This paper studies the problems of vehicle make & model classification. Some
of the main challenges are reaching high classification accuracy and reducing
the annotation time of the images. To address these problems, we have created a
fine-grained database using online vehicle marketplaces of Turkey. A pipeline
is proposed to combine an SSD (Single Shot Multibox Detector) model with a CNN
(Convolutional Neural Network) model to train on the database. In the pipeline,
we first detect the vehicles by following an algorithm which reduces the time
for annotation. Then, we feed them into the CNN model. It is reached
approximately 4% better classification accuracy result than using a
conventional CNN model. Next, we propose to use the detected vehicles as ground
truth bounding box (GTBB) of the images and feed them into an SSD model in
another pipeline. At this stage, it is reached reasonable classification
accuracy result without using perfectly shaped GTBB. Lastly, an application is
implemented in a use case by using our proposed pipelines. It detects the
unauthorized vehicles by comparing their license plate numbers and make &
models. It is assumed that license plates are readable.Comment: 10 pages, ICANN 2018: Artificial Neural Networks and Machine Learnin
Intensity dependences of the nonlinear optical excitation of plasmons in graphene
Recently, we demonstrated an all-optical coupling
scheme for plasmons, which takes advantage of the
intrinsic nonlinear optical response of graphene.
Frequency mixing using free-space, visible light
pulses generates surface plasmons in a planar
graphene sample, where the phase matching
condition can define both the wavevector and energy
of surface waves and intraband transitions. Here,
we also show that the plasmon generation process is
strongly intensity-dependent, with resonance features
washed out for absorbed pulse fluences greater than
0.1 J m−2. This implies a subtle interplay between the
nonlinear generation process and sample heating. We
discuss these effects in terms of a non-equilibrium
charge distribution using a two-temperature model.Peer ReviewedPostprint (author's final draft
The topological glass in ring polymers
We study the dynamics of concentrated, long, semi-flexible, unknotted and unlinked ring polymers embedded in a gel by Monte Carlo simulation of a coarse-grained model. This involves the ansatz that the rings compactify into a duplex structure where they can be modelled as linear polymers. The classical polymer glass transition involves a rapid loss of microscopic freedom within the polymer molecule as the temperature is reduced toward Tg. Here we are interested in temperatures well above Tg where the polymers retain high microscopic mobility. We analyse the slowing of stress relaxation originating from inter-ring penetrations (threadings). For long polymers an extended network of quasi-topological penetrations forms. The longest relaxation time appears to depend exponentially on the ring polymer contour length, reminiscent of the usual exponential slowing (e.g., with temperature) in classical glasses. Finally, we discuss how this represents a universality class for glassy dynamics
Spin-stripe density varies linearly with hole content in single-layer Bi2201 cuprate
We have performed inelastic neutron scattering measurements on the
single-layer cuprate Bi2+xSr2-xCuO6+y (Bi2201) with x=0.2, 0.3, 0.4 and 0.5, a
doping range that spans the spin-glass (SG) to superconducting (SC) phase
boundary. The doping evolution of low energy spin fluctuations was found to be
characterized by a change of incommensurate modulation wave vector from the
tetragonal [110] to [100]/[010] directions, while maintaining a linear relation
between the incommensurability and the hole concentration, delta p. In the SC
regime, the spectral weight is strongly suppressed below 4 meV. Similarities
and differences in the spin correlations between Bi2201 and the prototypical
single-layer system La2-xSrxCuO4 are discussed.Comment: 5 page,4 figure
Spin states and persistent currents in mesoscopic rings: spin-orbit interactions
We investigate theoretically electron spin states in one dimensional (1D) and
two dimensional (2D) hard-wall mesoscopic rings in the presence of both the
Rashba spin-orbit interaction (RSOI) and the Dresselhaus spin-orbit interaction
(DSOI) in a perpendicular magnetic field. The Hamiltonian of the RSOI alone is
mathematically equivalent to that of the DSOI alone using an SU(2) spin
rotation transformation. Our theoretical results show that the interplay
between the RSOI and DSOI results in an effective periodic potential, which
consequently leads to gaps in the energy spectrum. This periodic potential also
weakens and smoothens the oscillations of the persistent charge current (CC)
and spin current (SC) and results in the localization of electrons. For a 2D
ring with a finite width, higher radial modes destroy the periodic oscillations
of persistent currents.Comment: 12 pages, 14 figure
CP Asymmetry in Charged Higgs Decays to Chargino-Neutralino
We analyze the charge-parity (CP) asymmetry in the charged Higgs boson decays
to chargino-neutralino pairs, H^- -> chargino_i + neutralino_j. We show first
that these modes have a large branching ratio for m_H^- > 600 GeV. We use
Cutkosky rules to obtain the analytical formulas needed for the evaluation of
the asymmetry under consideration. We then calculate the CP asymmetry in
chargino-neutralino decays by including supersymmetric mass bounds, as well as
constraints from b -> s gamma, (g-2)_mu, Delta\rho and electric dipole moments.
Finally, we discuss observability of the asymmetry at the LHC by calculating
the number of required charged Higgs events to observe the asymmetry for each
decay channel. We show that the inclusion of constraints considerably reduces
the projected CP asymmetry, and that the optimal channel for observing the
asymmetry is H^- -> chargino_1 + neutralino_2.Comment: 23 pages, 8 figures, one tabl
Kinetics of natural aging in Al-Mg-Si alloys studied by positron annihilation lifetime spectroscopy
The process of natural aging in pure ternary Al-Mg-Si alloys was studied by
positron annihilation lifetime spectroscopy in real time in order to clarify
the sequence and kinetics of clustering and precipitation. It was found that
natural aging takes place in at least five stages in these alloys, four of
which were directly observed. This is interpreted as the result of complex
interactions between vacancies and solute atoms or clusters. One of the early
stages of positron lifetime evolution coincides with a clustering process
observed by differential scanning calorimetry (DSC) and involves the formation
of a positron trap with \sim 0.200 ns lifetime. In later stages, a positron
trap with a higher lifetime develops in coincidence with the DSC signal of a
second clustering reaction. Mg governs both the kinetics and the lifetime
change in this stage. Within the first 10 min after quenching, a period of
nearly constant positron lifetime was found for those Mg-rich alloys that later
show an insufficient hardness response to artificial aging, the so-called
"negative effect." The various processes observed could be described by two
effective activation energies that were found by varying the aging temperature
from 10 to 37\degree C.Comment: arXiv admin note: same as v2, to correct mistaken v
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