465 research outputs found
Overcomplete steerable pyramid filters and rotation invariance
A given (overcomplete) discrete oriented pyramid may be converted into a steerable pyramid by interpolation. We present a technique for deriving the optimal interpolation functions (otherwise called 'steering coefficients'). The proposed scheme is demonstrated on a computationally efficient oriented pyramid, which is a variation on the Burt and Adelson (1983) pyramid. We apply the generated steerable pyramid to orientation-invariant texture analysis in order to demonstrate its excellent rotational isotropy. High classification rates and precise rotation identification are demonstrated
Long term Ultra-Violet Variability of Seyfert galaxies
Flux variability is one of the defining characteristics of Seyfert galaxies,
a class of active galactic nuclei (AGN). Though these variations are observed
over a wide range of wavelengths, results on their flux variability
characteristics in the ultra-violet (UV) band are very limited. We present here
the long term UV flux variability characteristics of a sample of fourteen
Seyfert galaxies using data from the International Ultraviolet Explorer
acquired between 1978 and 1995. We found that all the sources showed flux
variations with no statistically significant difference in the amplitude of UV
flux variation between shorter and longer wavelengths. Also, the flux
variations between different near-UV (NUV, 1850 - 3300 A) and far-UV (FUV, 1150
- 2000 A) passbands in the rest frames of the objects are correlated with no
time lag. The data show indications of (i) a mild negative correlation of UV
variability with bolometric luminosity and (ii) weak positive correlation
between UV variability and black hole mass. At FUV, about 50% of the sources
show a strong correlation between spectral indices and flux variations with a
hardening when brightening behaviour, while for the remaining sources the
correlation is moderate. In NUV, the sources do show a harder when brighter
trend, however, the correlation is either weak or moderate.Comment: Accepted by Journal of Astrophysics and Astronom
8 GHz Tunable Gunn Oscillator in WR-137 Waveguide
The conventional technique of realising waveguide resonators for Gunn diode oscillators to operate at the band edge of the waveguide fails owing to the excitation of a coaxial mode resonance formed by the post and the side walls of the waveguide. One of the solutions to the problem is to mount the diode in a ridged waveguide resonator. This has been demonstrated by constructing an 8 GHz Gunn oscillator using a single ridge in WR-137 waveguide.The steps in designing the oscillator system are also presented
Suppression of power-broadening in strong-coupling photoassociation in the presence of a Feshbach resonance
Photoassociation (PA) spectrum in the presence of a magnetic Feshbach
resonance is analyzed. Nonperturbative solution of the problem yields
analytical expressions for PA linewidth and shift which are applicable for
arbitrary PA laser intensity and magnetic field tuning of Feshbach Resonance.
We show that by tuning magnetic field close to Fano minimum, it is possible to
suppress power broadening at increased laser intensities. This occurs due to
quantum interference of PA transitions from unperturbed and perturbed
continuum. Line narrowing at high laser intensities is accompanied by large
spectral shifts. We briefly discuss important consequences of line narrowing in
cold collisions.Comment: 12 pages, 5 figure
Role of soluble, cell wall bound phenolics, tannin and flavonoid contents in maize resistance to pink stem borer Sesamia inferens Walker
The pink stem borer Sesamia inferens Walker is an important pest of winter maize which causes significant yieldlosses. In an attempt to identify the biochemical basis of resistance against S. inferens, total soluble phenolics, boundphenolics, cell wall-bound hydroxycinnamic acids-p-coumaric acid (p-CA), ferulic acid (FA), total tannin contentand total flavonoid contents, were measured in leaf at 10, 20 days after germination (DAG); stem at 20, 40 DAG;pith and rind tissues at 60 DAG (stem differentiated). From the present study, it was found that bound phenolics,p-CA, ferulic acid and total tannin contents contribute to the maize defense mechanism against S. inferens. Totalbound phenolic content showed negative correlation with Leaf Injury Rating (LIR). Highly significant strong positivecorrelation (+0.9750) was observed between LIR and total soluble phenolics in leaf tissue at 20 DAG. Similarlyhighly significant strong positive correlation between LIR and total tannins (+0.9354**) and flavonoids (+0.9582**)in pith at 60 DAG was observed. Further, a strong significant positive correlation was also observed between LIRand p-CA (+0.9199*) in pith at 60 DAG and total ferulic acid (+0.9051*) in rind at 60 DAG. The significant strong negativecorrelation between LIR and p-CA (-0.8441*) in stem at 40 DAG was observed. The total bound phenolicsin rind at 60 DAG (0.756), in leaf at 20 DAG (0.681), and total soluble phenolics in the stem at 20 DAG (0.685) showedhigher loadings with PC1, PC2, and PC3, respectively. Genotype-by-biochemical factor biplot showed that thedata of biochemical parameters measured in different tissues and stages could be able to group the genotypesaccording to their reaction to S. inferens
Long-term optical and infrared variability characteristics of Fermi blazars
We present long-term optical and near-infrared flux variability analysis of 37 blazars detected in the gamma-ray band by the Fermi Gamma-Ray Space Telescope. Among them, 30 are flat spectrum radio quasars (FSRQs) and 7 are BL Lac objects (BL Lacs). The photometric data in the optical (BVR) and infrared (JK) bands were from the Small and Moderate Aperture Research Telescope System acquired between 2008-2018. From cross-correlation analysis of the light curves at different wavelengths, we did not find significant time delays between variations at different wavelengths, except for three sources, namely PKS 1144-379, PKS B1424-418, and 3C 273. For the blazars with both B- and J-band data, we found that in a majority of FSRQs and BL Lacs, the amplitude of variability (sigma(m)) in the J band is larger than that in B band, consistent with the dominance of the non-thermal jet over the thermal accretion disc component. Considering FSRQs and BL Lacs as a sample, there are indications of sigma(m) to increase gradually towards longer wavelengths in both, however, found to be statistically significant only between B and J bands in FSRQs. In the B - J v/s J-colour magnitude diagram, we noticed complicated spectral variability patterns. Most of the objects showed a redder when brighter (RWB) behaviour. Few objects showed a bluer when brighter (BWB) trend, while in some objects both BWB and RWB behaviours were noticed. These results on flux and colour characteristics indicate that the jet emission of FSRQs and BL Lacs is indistinguishable
Cosmological constraints on R-parity violation from neutrino decay
If the neutrino mass is non-zero, as hinted by several experiments, then
R-parity-violating supersymmetric Yukawa couplings can drive a heavy neutrino
decay into lighter states. The heavy neutrino may either decay radiatively into
a lighter neutrino, or it may decay into three light neutrinos through a
Z-mediated penguin. For a given mass of the decaying neutrino, we calculate its
lifetime for the various modes, each mode requiring certain pairs of
R-parity-violating couplings be non-zero. We then check whether the calculated
lifetimes fall in zones allowed or excluded by cosmological requirements. For
the latter case, we derive stringent new constraints on the corresponding
products of R-parity-violating couplings for given values of the decaying
neutrino mass.Comment: 13 pages, Latex, uses axodraw.sty; version to appear in Physical
Review
Classical Spin Models with Broken Continuous Symmetry: Random Field Induced Order and Persistence of Spontaneous Magnetization
We consider a classical spin model, of two-dimensional spins, with continuous
symmetry, and investigate the effect of a symmetry breaking unidirectional
quenched disorder on the magnetization of the system. We work in the mean field
regime. We show, by numerical simulations and by perturbative calculations in
the low as well as in the high temperature limits, that although the continuous
symmetry of the magnetization is lost, the system still magnetizes, albeit with
a lower value as compared to the case without disorder. The critical
temperature at which the system starts magnetizing, also decreases with the
introduction of disorder. However, with the introduction of an additional
constant magnetic field, the component of magnetization in the direction that
is transverse to the disorder field increases with the introduction of the
quenched disorder. We discuss the same effects also for three-dimensional
spins.Comment: 12 pages, 12 figures, RevTeX
Spontaneous R-Parity Violation, Flavor Symmetry and Tribimaximal Mixing
We explore the possibility of spontaneous R parity violation in the context
of flavor symmetry. Our model contains singlet matter chiral superfields which are arranged as triplet of
and as well as few additional Higgs chiral superfields which are singlet
under MSSM gauge group and belong to triplet and singlet representation under
the flavor symmetry. R parity is broken spontaneously by the vacuum
expectation values of the different sneutrino fields and hence we have
neutrino-neutralino as well as neutrino-MSSM gauge singlet higgsino mixings in
our model, in addition to the standard model neutrino- gauge singlet neutrino,
gaugino-higgsino and higgsino-higgsino mixings. Because all of these mixings we
have an extended neutral fermion mass matrix. We explore the low energy
neutrino mass matrix for our model and point out that with some specific
constraints between the sneutrino vacuum expectation values as well as the MSSM
gauge singlet Higgs vacuum expectation values, the low energy neutrino mass
matrix will lead to a tribimaximal mixing matrix. We also analyze the potential
minimization for our model and show that one can realize a higher vacuum
expectation value of the singlet
sneutrino fields even when the other sneutrino vacuum expectation values are
extremely small or even zero.Comment: 18 page
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