Smear correction of highly-variable, frame-transfer-CCD images with application to polarimetry

Image smear, produced by the shutter-less operation of frame transfer CCD detectors, can be detrimental for many imaging applications. Existing algorithms used to numerically remove smear, do not contemplate cases where intensity levels change considerably between consecutive frame exposures. In this report we reformulate the smearing model to include specific variations of the sensor illumination. The corresponding desmearing expression and its noise properties are also presented and demonstrated in the context of fast imaging polarimetry.Comment: Article accepted for publication in Applied Optics on 08 Jun 201

Size-dependent magnetization fluctuations in NiO nanoparticles

The finite size and surface roughness effects on the magnetization of NiO nanoparticles is investigated. A large magnetic moment arises for an antiferromagnetic nanoparticle due to these effects. The magnetic moment without the surface roughness has a non-monotonic and oscillatory dependence on $R$, the size of the particles, with the amplitude of the fluctuations varying linearly with $R$. The geometry of the particle also matters a lot in the calculation of the net magnetic moment. An oblate spheroid shape particle shows an increase in net magnetic moment by increasing oblateness of the particle. However, the magnetic moment values thus calculated are very small compared to the experimental values for various sizes, indicating that the bulk antiferromagnetic structure may not hold near the surface. We incorporate the surface roughness in two different ways; an ordered surface with surface spins inside a surface roughness shell aligned due to an internal field, and a disordered surface with randomly oriented spins inside surface roughness shell. Taking a variational approach we find that the core interaction strength is modified for nontrivial values of $\Delta$ which is a signature of multi-sublattice ordering for nanoparticles. The surface roughness scale $\Delta$ is also showing size dependent fluctuations, with an envelope decay $\Delta\sim R^{-1/5}$. The net magnetic moment values calculated using spheroidal shape and ordered surface are close to the experimental values for different sizes.Comment: 19 pages, 8 figures, Accepted for publication in Int. J. Mod. Phys.

M dwarfs in the b201 tile of the VVV survey: Colour-based Selection, Spectral Types and Light Curves

The intrinsically faint M dwarfs are the most numerous stars in the Galaxy, have main-sequence lifetimes longer than the Hubble time, and host some of the most interesting planetary systems known to date. Their identification and classification throughout the Galaxy is crucial to unravel the processes involved in the formation of planets, stars and the Milky Way. The ESO Public Survey VVV is a deep near-IR survey mapping the Galactic bulge and southern plane. The VVV b201 tile, located in the border of the bulge, was specifically selected for the characterisation of M dwarfs. We used VISTA photometry to identify M dwarfs in the VVV b201 tile, to estimate their subtypes, and to search for transit-like light curves from the first 26 epochs of the survey. UKIDSS photometry from SDSS spectroscopically identified M dwarfs was used to calculate their expected colours in the $YJHK_s$ VISTA system. A colour-based spectral subtype calibration was computed. Possible giants were identified by a $(J-K_s, H_{J})$ reduced proper motion diagram. The light curves of 12.8<$K_s$<15.8 colour-selected M dwarfs were inspected for signals consistent with transiting objects. We identified 23,345 objects in VVV b201 with colours consistent with M dwarfs. We provided their spectral types and photometric distances, up to $\sim$ 300 pc for M9s and $\sim$ 1.2 kpc for M4s, from photometry. In the range 12<$K_s$<16, we identified 753 stars as possible giants out of 9,232 M dwarf candidates. While only the first 26 epochs of VVV were available, and 1 epoch was excluded, we were already able to identify transit-like signals in the light curves of 95 M dwarfs and of 12 possible giants. Thanks to its deeper photometry ($\sim$4 magnitudes deeper than 2MASS), the VVV survey will be a major contributor to the discovery and study of M dwarfs and possible companions towards the center of the Milky Way.Comment: 11 pages, 4 figures. Accepted for publication in Catalogs and data of Astronomy and Astrophysic

Riemann-Langevin Particle Filtering in Track-Before-Detect

Track-before-detect (TBD) is a powerful approach that consists in providing the tracker with sensor measurements directly without pre-detection. Due to the measurement model non-linearities, online state estimation in TBD is most commonly solved via particle filtering. Existing particle filters for TBD do not incorporate measurement information in their proposal distribution. The Langevin Monte Carlo (LMC) is a sampling method whose proposal is able to exploit all available knowledge of the posterior (that is, both prior and measurement information). This letter synthesizes recent advances in LMC-based filtering to describe the Riemann-Langevin particle filter and introduces its novel application to TBD. The benefits of our approach are illustrated in a challenging low-noise scenario.Comment: Minor grammatical update

Income Distribution Dependence of Poverty Measure: A Theoretical Analysis

With a new deprivation (or poverty) function, in this paper, we theoretically study the changes in poverty with respect to the `global' mean and variance of the income distribution using Indian survey data. We show that when the income obeys a log-normal distribution, a rising mean income generally indicates a reduction in poverty while an increase in the variance of the income distribution increases poverty. This altruistic view for a developing economy, however, is not tenable anymore once the poverty index is found to follow a pareto distribution. Here although a rising mean income indicates a reduction in poverty, due to the presence of an inflexion point in the poverty function, there is a critical value of the variance below which poverty decreases with increasing variance while beyond this value, poverty undergoes a steep increase followed by a decrease with respect to higher variance. Following these results, we make quantitative predictions to correlate a developing with a developed economy.Comment: 13 pages in single spaced latex, 4 figures, submitted to 'Econometrica

Effects of dust scattering albedo and 2175 A bump on ultraviolet colours of normal disc galaxies

We discuss dust properties in the interstellar medium (ISM) of nearby normal galaxies, by comparing observations in the ultraviolet (UV) with simulations by a radiative transfer model. The observed UV colours of nearby galaxies show a reddening relative to their expected intrinsic colours. Some authors argued that the Milky Way dust cannot reproduce the reddening because of the prominent 2175 \AA absorption bump. Other authors proposed a reduction mechanism of the bump strength in an {\it attenuation law} derived from the ratio of the observed intensity to the intrinsic one through an age-selective attenuation (i.e., young stars are more attenuated selectively). We newly find that the wavelength dependence of the scattering albedo also has a strong effect on the UV colour; an albedo decreasing toward shorter wavelengths (except for the absorption bump range) produces a significant UV reddening. After comparing the observed UV colours of nearby normal galaxies with those expected from radiative transfer simulations assumed several dust models, we find two sorts of dust suitable for these galaxies: (1) dust with a bump and a smaller albedo for a shorter wavelength (except for the bump range), and (2) dust without any bump but with an almost constant albedo. If very small carbonaceous grains responsible for the common unidentified infrared emission band are also the bump carrier, the former dust is favorable. Finally, we derive mean attenuation laws of various dust models as a function of the UV attenuation, and derive some relations between the UV attenuation and observable/theoretical quantities.Comment: MNRAS in pres

Magnetic structure and orbital ordering in BaCoO3 from first-principles calculations

Ab initio calculations using the APW+lo method as implemented in the WIEN2k code have been used to describe the electronic structure of the quasi-one-dimensional system BaCoO3. Both, GGA and LDA+U approximations were employed to study different orbital and magnetic orderings. GGA predicts a metallic ground state whereas LDA+U calculations yield an insulating and ferromagnetic ground state (in a low-spin state) with an alternating orbital ordering along the Co-Co chains, consistent with the available experimental data.Comment: 8 pages, 9 figure

The Quest for Palladium-Catalysed Alkyl-Nitrogen Bond Formation

Our interest in the development of transition-metal catalysis for the realisation of vicinal diamination reactions of alkenes started about a decade ago. A number of successful transformations in this area have been developed using palladium catalysis. As a challenging aspect of major importance, the palladium-catalysed coupling of alkyl–nitrogen bonds constitutes the second step in diaminations of alkenes. We here discuss the details that led us to consider high-oxidation-state palladium catalysis as a key feature in such C–N bond-forming reactions. This work discusses both our own contributions and the ones from colleagues and combines the discussion of catalytic reactions and stoichiometric control experiments. It demonstrates that reductive alkyl–nitrogen bond formation from palladium(IV) proceeds with a low activation barrier and through a linear transition state of nucleophilic displacement