Multi-frequency observations and spectral analysis of two gigahertz-peaked spectra pulsars

We report the multi-frequency observations of two pulsars: J1740+1000 and B1800-21, using the Giant Metrewave Radio Telescope and the Green Bank Telescope. The main aim of these observations was to estimate the flux density spectrum of these pulsars, as both of them were previously reported to exhibit gigahertz-peaked spectra. J1740+1000 is a young pulsar far from the Galactic plane and the interpretation of its spectrum was inconclusive in the light of the recent flux density measurements. Our result supports the gigahertz-peaked interpretation of the PSR J1740+1000 spectrum. B1800-21 is a Vela-like pulsar near the W30 complex, whose spectrum exhibit a significant change between 2012 and 2014 year. Our analysis shows that the current shape of the spectrum is similar to that observed before 2009 and confirms that the observed spectral change happen in a time-scale of a few years.Comment: 9 pages, 7 figure

Gigahertz-peaked spectra pulsars and thermal absorption model

We present the results of our radio interferometric observations of pulsars at 325 MHz and 610 MHz using the Giant Metrewave Radio Telescope (GMRT). We used the imaging method to estimate the flux densities of several pulsars at these radio frequencies. The analysis of the shapes of the pulsar spectra allowed us to identify five new gigahertz-peaked spectra (GPS) pulsars. Using the hypothesis that the spectral turnovers are caused by thermal free-free absorption in the interstellar medium, we modeled the spectra of all known objects of this kind. Using the model, we were able to put some observational constrains on the physical parameters of the absorbing matter, which allows us to distinguish between the possible sources of absorption. We also discuss the possible effects of the existence of GPS pulsars on future search surveys, showing that the optimal frequency range for finding such objects would be from a few GHz (for regular GPS sources) to possibly 10 GHz for pulsars and radio-magnetars exhibiting very strong absorption.Comment: Accepted for publication in ApJ, 28 pages, 8 figure

Approximation of corner polyhedra with families of intersection cuts

We study the problem of approximating the corner polyhedron using intersection cuts derived from families of lattice-free sets in $\mathbb{R}^n$. In particular, we look at the problem of characterizing families that approximate the corner polyhedron up to a constant factor, which depends only on $n$ and not the data or dimension of the corner polyhedron. The literature already contains several results in this direction. In this paper, we use the maximum number of facets of lattice-free sets in a family as a measure of its complexity and precisely characterize the level of complexity of a family required for constant factor approximations. As one of the main results, we show that, for each natural number $n$, a corner polyhedron with $n$ basic integer variables and an arbitrary number of continuous non-basic variables is approximated up to a constant factor by intersection cuts from lattice-free sets with at most $i$ facets if $i> 2^{n-1}$ and that no such approximation is possible if $i \leq 2^{n-1}$. When the approximation factor is allowed to depend on the denominator of the fractional vertex of the linear relaxation of the corner polyhedron, we show that the threshold is $i > n$ versus $i \leq n$. The tools introduced for proving such results are of independent interest for studying intersection cuts

Modified Bethe-Weizsacker mass formula with isotonic shift and new driplines

Nuclear masses are calculated using the modified Bethe-Weizsacker mass formula in which the isotonic shifts have been incorporated. The results are compared with the improved liquid drop model with isotonic shift. Mass excesses predicted by this method compares well with the microscopic-macroscopic model while being much more simple. The neutron and proton drip lines have been predicted using this modified Bethe-Weizsacker mass formula with isotonic shifts.Comment: 9 pages including 2 figure

Symbolic Implementation of Connectors in BIP

BIP is a component framework for constructing systems by superposing three layers of modeling: Behavior, Interaction, and Priority. Behavior is represented by labeled transition systems communicating through ports. Interactions are sets of ports. A synchronization between components is possible through the interactions specified by a set of connectors. When several interactions are possible, priorities allow to restrict the non-determinism by choosing an interaction, which is maximal according to some given strict partial order. The BIP component framework has been implemented in a language and a tool-set. The execution of a BIP program is driven by a dedicated engine, which has access to the set of connectors and priority model of the program. A key performance issue is the computation of the set of possible interactions of the BIP program from a given state. Currently, the choice of the interaction to be executed involves a costly exploration of enumerative representations for connectors. This leads to a considerable overhead in execution times. In this paper, we propose a symbolic implementation of the execution model of BIP, which drastically reduces this overhead. The symbolic implementation is based on computing boolean representation for components, connectors, and priorities with an existing BDD package

Selectively strong coupling MoS2_2 excitons to a metamaterial at room temperature

Light emitters in vicinity of a hyperbolic metamaterial (HMM) show a range of quantum optical phenomena from spontaneous decay rate enhancement to strong coupling. In this study, we integrate monolayer Molybdenum disulfide (MoS$_2$) emitter in near field region of HMM. The MoS$_2$ monolayer has A and B excitons, which emit in the red region of visible spectrum. We find that the B excitons couple to HMM differently compared to A excitons. The fabricated HMM transforms to a hyperbolic dispersive medium at 2.13 eV, from an elliptical dispersive medium. The selective coupling of B Excitons to the HMM modes is attributed to the inbuilt field gradient of the transition. The B exciton energy lies close to the transition point of the HMM, relative to A Exciton. So, the HMM modes couple more to the B excitons and the metamaterial functions as selective coupler. The coupling strength calculations show that coupling is 2.5 times stronger for B excitons relative to A excitons. High near field of HMM, large magnitude and the in-plane transition dipole moment of MoS$_2$ Excitons, result in strong coupling of B excitons and formation of hybrid light-matter states. The measured differential Reflection and Photoluminescence spectra indicate the presence of hybrid light-matter states i.e. Exciton-Polaritons. Rabi splitting of at least 129 meV at room temperature is observed. The low temperature Photoluminescence measurement shows mode anticrossing, which is characteristic feature of hybrid states. Our results show that the HMM works as a energy selective coupler for multi-excitonic systems as MoS$_2$

Ion Beam Based Techniques for Mercury Cadmium Telluride Infrared Detectors

The paper reviews the applications of ion beam-based techniques such as ion implantation and ion beam milling, for HgCdTe detector fabrication. Fabrication of large-format arrays and two-color arrays necessitate the use of dry processes. Ion irradiation causes type conversion in HgCdTe. The type conversion is far beyond the damage sites because of Hg in-diffusion to interstitial sites. The dry processes combine high anisotropy, faster etch rates, and better dimensional control, than wet etch processes, but require the damaged region to be removed.Defence Science Journal, 2009, 59(4), pp.395-400, DOI:http://dx.doi.org/10.14429/dsj.59.153

Comparative Solubility of Protein in Cottonseed Flakes Extracted by Hexane and by Ethanol at Two Different Temperatures

The solubility in water, in 3 percent sodium chloride solution, and in 0.2 N sodium hydroxide solution of cottonseed flakes extracted by ethanol at 172° F. is lower than similar flakes extracted by hexane at 146° F. Data are presented which indicate the lower solubility is mainly the result of the differences in the solvents rather than the temperatures. The difference in solubility in the sodium hydroxide solution is less than in the sodium chloride solution