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