5,910 research outputs found
The quiescent progenitors of four Type II-P/L supernovae
We present Large Binocular Telescope difference imaging data for the final
years of four Type II-P/L supernovae progenitors. For all four, we find no
significant evidence for stochastic or steady variability in the U, B, V, or
R-bands. Our limits constrain variability to no more than roughly 5-10% of the
expected R-band luminosities of the progenitors. These limits are comparable to
the observed variability of red supergiants in the Magellanic Clouds. Based on
these four events, the probability of a Type II-P/L progenitor having an
extended outburst after Oxygen ignition is <37% at 90% confidence. Our
observations cannot exclude short outbursts in which the progenitor returns to
within ~10% of its quiescent flux on the time scale of months with no dust
formation.Comment: 9 pages, 8 figures, 1 table. Accepted to MNRA
Excited ionic and neutral fragments produced by dissociation of the N2(+)* H band
N I and N II fluorescent radiation was observed when N2 was irradiated by undispersed synchrotron radiation with an upper energy limit of approximately 200 eV. The excited fragments originate from dissociation of a band of excited ionic states of N2 lying between 34.7 and 44 eV
Accurate photoionisation cross section for He at non-resonant photon energies
The total single-photon ionisation cross section was calculated for helium
atoms in their ground state. Using a full configuration-interaction approach
the photoionisation cross section was extracted from the complex-scaled
resolvent. In the energy range from ionisation threshold to 59\,eV our results
agree with an earlier -spline based calculation in which the continuum is
box discretised within a relative error of in the non-resonant part of
the spectrum. Above the \He^{++} threshold our results agree on the other
hand very well to a recent Floquet calculation. Thus our calculation confirms
the previously reported deviations from the experimental reference data outside
the claimed error estimate. In order to extend the calculated spectrum to very
high energies, an analytical hydrogenic-type model tail is introduced that
should become asymptotically exact for infinite photon energies. Its
universality is investigated considering also H, Li, and HeH. With
the aid of the tail corrections to the dipole approximation are estimated.Comment: 20 pages, 7 figures, 2 table
Unsupervised Segmentation of Action Segments in Egocentric Videos using Gaze
Unsupervised segmentation of action segments in egocentric videos is a
desirable feature in tasks such as activity recognition and content-based video
retrieval. Reducing the search space into a finite set of action segments
facilitates a faster and less noisy matching. However, there exist a
substantial gap in machine understanding of natural temporal cuts during a
continuous human activity. This work reports on a novel gaze-based approach for
segmenting action segments in videos captured using an egocentric camera. Gaze
is used to locate the region-of-interest inside a frame. By tracking two simple
motion-based parameters inside successive regions-of-interest, we discover a
finite set of temporal cuts. We present several results using combinations (of
the two parameters) on a dataset, i.e., BRISGAZE-ACTIONS. The dataset contains
egocentric videos depicting several daily-living activities. The quality of the
temporal cuts is further improved by implementing two entropy measures.Comment: To appear in 2017 IEEE International Conference On Signal and Image
Processing Application
COVID-19 Pandemic and Volatility Persistence of the Nigerian Crude Oil Price
Impacts of COVID-19 pandemic on the global economy cannot be overemphasized, especially with Nigeria, which largely depends on crude oil as a major source of her revenue. Thus, investigating COVID-19’s impacts on the volatility persistence of Nigerian crude oil price forms the nucleus of this study. Our modelling framework was based on GARCH, EGARCH and GJR-GARCH with two asymmetric innovation distributions Daily price data on the Nigerian crude oil sales (in dollars per barrel), ranging from 4th Jan., 2010 to 27th May, 2021, were obtained from the Central Bank of Nigeria (CBN). To capture the impact of the pandemic, the data were divided into two periods, before Covid-19 was proscribed as a pandemic by World Health Organisation (01/04/2010 to 10/03/2020) and during COVID-19 pandemic (11/03/2020 to 27/05/2021). Result shows that the leverage effect were positive and significant in both periods which indicates that positive shocks increases volatility more than negative news of the same sign. Also, EGARCH-SSTD and GJR-GARCH (1,1)-SSTD were the best fitted models for before and during pandemic respectively. Result shows that volatility persistence was higher during COVID-19 period (1.012639) than before the COVID-19 pandemic (0.988749) .There was also an increase and over persistence in the volatility of Nigerian crude oil price during COVID-19 than before COVID-19 period
Tunable refraction in a two dimensional quantum metamaterial
In this paper we consider a two-dimensional metamaterial comprising an array
of qubits (two level quantum objects). Here we show that a two-dimensional
quantum metamaterial may be controlled, e.g. via the application of a magnetic
flux, so as to provide controllable refraction of an input signal. Our results
are consistent with a material that could be quantum birefringent (beam
splitter) or not dependent on the application of this control parameter. We
note that quantum metamaterials as proposed here may be fabricated from a
variety of current candidate technologies from superconducting qubits to
quantum dots. Thus the ideas proposed in this work would be readily testable in
existing state of the art laboratories.Comment: 4 pages, 2 figure
Financial Development and Economic Growth in Nigeria: The Case Study of Nigeria
The study analyzed the effect of financial development on economic growth in Nigeria using time series data on annual growth rate of gross domestic product, real interest rate, the ratio of gross domestic savings to GDP, ratio of domestic credit to private sector to GDP over the period 1980 and 2019. While the variables real interest rate, the ratio of gross domestic savings to GDP, ratio of domestic credit to private sector to GDP served as explanatory variable, annual growth rate of gross domestic product was used as the dependent variable. The results indicated that two of the variables (real interest rate, gross domestic savings) are inversely related to the dependent variable (GDP annual growth rate) when combined together while domestic credit to private sector is positively related to the dependent variable with the coefficient of multiple determination showing that the model is of high good fit with approximately 93% of gross domestic product being explained by the variables included in the model, while the remaining 7% are factors inducing growth but were not captured in the model. Thus, the study, therefore, concluded that there is the need to adequately deepen the financial system through innovations, adequate and effective regulation and supervision, efficient mobilization of funds and making such funds available for productive investment, and improved services in order to propel economic growth
Hyperoxidation: influence of various oxygen supply levels on oxidation kinetics of phenolic compounds and wine quality
Chenin blanc, Mauzac and Chardonnay musts were hyperoxidized using three different oxygen levels fixed according to the maximum oxygen consumption capacity determined for each must. Phenolic composition of the control and oxidized musts and that of the corresponding wines were analyzed by HPLC. The wines were also submitted to sensory evaluation. Hyperoxidation hardly modified phenolic composition of Chenin blanc and Mauzac musts which were in fact almost totally oxidized after pressing. As well, it induced no change in wine quality in these two varieties. In Chardonnay musts, concentrations of caffeoyl and p-coumaroyl tartaric acid, 2-S-glutathionyl caffeoyl tartaric acid and catechin decreased with increasing oxygen supplies. Wines contained larger amounts of phenolic compounds than musts because part of the quinones formed during oxidation were reduced when sulfiting, especially for intemediate oxygen levels. Thus, sulfiting should be omitted or delayed to allow quinone condensation and maximum efficency of the hyperoxidation technique. Hyperoxidized Chardonnay wines were rated higher in quality and lower in color than the control
Self-Organization in Multimode Microwave Phonon Laser (Phaser): Experimental Observation of Spin-Phonon Cooperative Motions
An unusual nonlinear resonance was experimentally observed in a ruby phonon
laser (phaser) operating at 9 GHz with an electromagnetic pumping at 23 GHz.
The resonance is manifested by very slow cooperative self-detunings in the
microwave spectra of stimulated phonon emission when pumping is modulated at a
superlow frequency (less than 10 Hz). During the self-detuning cycle new and
new narrow phonon modes are sequentially ``fired'' on one side of the spectrum
and approximately the same number of modes are ``extinguished'' on the other
side, up to a complete generation breakdown in a certain final portion of the
frequency axis. This is usually followed by a short-time refractority, after
which the generation is fired again in the opposite (starting) portion of the
frequency axis. The entire process of such cooperative spectral motions is
repeated with high degree of regularity. The self-detuning period strongly
depends on difference between the modulation frequency and the resonance
frequency. This period is incommensurable with period of modulation. It
increases to very large values (more than 100 s) when pointed difference is
less than 0.05 Hz. The revealed phenomenon is a kind of global spin-phonon
self- organization. All microwave modes of phonon laser oscillate with the same
period, but with different, strongly determined phase shifts - as in optical
lasers with antiphase motions.Comment: LaTeX2e file (REVTeX4), 5 pages, 5 Postscript figures. Extended and
revised version of journal publication. More convenient terminology is used.
Many new bibliographic references are added, including main early theoretical
and experimental papers on microwave phonon lasers (in English and in
Russian
- …