bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification and characterization of the nano‐sized vesicles released by muscle cells
Authors: Romancino Daniele P. , Paterniti Gaetano , Campos Yvan , De Luca Angela , Di Felice Valentina , d'Azzo Alessandra , Bongiovanni Antonella
Published: March 2013

Several cell types secrete small membranous vesicles that contain cell‐specific collections of proteins, lipids, and genetic material. The function of these vesicles is to allow cell‐to‐cell signaling and the horizontal transfer of their cargo molecules. Here, we demonstrate that muscle cells secrete nano‐sized vesicles and that their release increases during muscle differentiation. Analysis of these nanovesicles allowed us to characterize them as exosome‐like particles and to define the potential role of the multifunctional protein Alix in their biogenesis.
MicroRNA‐155 is a novel suppressor of ovarian cancer‐initiating cells that targets CLDN1
Authors: Qin Wenxing , Ren Qiusheng , Liu Te , Huang Yongyi , Wang Jiejun
Published: March 2013

Previous cDNA microarrays indicated that CLDN1 (claudin‐1) is an important gene for ovarian cancer‐initiating cell (OCIC) invasion and adhesion. Here, we show that the downregulation of miR‐155 in OCICs correlates with CLDN1 overexpression and the suppression of OCIC invasion. Luciferase assays indicate that miR‐155 targets CLDN1 mRNA on the 3′ UTR. CLDN1 mRNA and claudin‐1 protein expression were significantly decreased in miR‐155‐OCICs. Proliferation assays and Transwell migration assays show that miR‐155 significantly suppresses the proliferative and invasive capacity of OCICs. Furthermore, miR‐155 suppresses the growth of OCIC xenograft tumors. Thus, overexpression of miR‐155 may prevent tumorigenesis in human ovarian cancer through downregulation of CLDN1.
Squirals and beyond: substitution tilings with singular continuous spectrum
Authors: BAAKE MICHAEL , GRIMM UWE
Published: March 2013

The squiral inflation rule is equivalent to a bijective block substitution rule and leads to an interesting lattice dynamical system under the action of${ \mathbb{Z} }^{2} $. In particular, its balanced version has purely singular continuous diffraction. The dynamical spectrum is of mixed type, with pure point and singular continuous components. We present a constructive proof that admits a generalization to bijective block substitutions of trivial height on${ \mathbb{Z} }^{d} $.
HUMAN RESOURCE CAPACITY TO EFFECTIVELY IMPLEMENT MALARIA ELIMINATION: A POLICY BRIEF FOR ETHIOPIA
Authors: Woyessa Adugna , Hadis Mamuye , Kebede Amha
Published: March 2013

Objective: The aim of this study was to investigate malaria elimination in Ethiopia. Ethiopia has planned to eliminate malaria by 2015 in areas of unstable malaria transmission and in the entire country by 2020. However, there is a shortage and maldistribution of the health workforce in general and malaria experts in particular. Training, motivating, and retaining the health workforce involved in malaria control is one strategy to address the shortage and maldistribution of the health workforce to achieve the goal of elimination.

Methods: Policy options include the following: (i) in-service training (educational outreach visits, continuing education meetings and workshops, audit and feedback, tailored interventions, and guideline dissemination) may improve professional practice; (ii) recruiting and training malaria specialists together with academic support, career guidance, and social support may increase the number of malaria experts; and (iii) motivation and retention packages (such as financial, educational, personal, and professional support incentives) may help motivate and retain malaria professionals.

Results: Implementation strategies include the following: (i) massive training of health personnel involved in malaria elimination and malaria experts (requiring special training) at different levels (national, sub-national, District & community levels), and (ii) recruiting highly qualified health personnel and retention and motivation mechanisms are needed.

Conclusions: The lack of adequately trained human resources and personnel attrition are major challenges to effectively implement the planned multi-faceted malaria elimination by 2020 strategy in Ethiopia. Although a reduction in malaria incidence has been observed in the last 3-4 years, maintaining this success and achieving the malaria elimination goal with the present human resource profile will be impossible. A clear strategy for developing the capacity of the health workers in general, and malaria experts in particular, and retaining and motivating staff are crucial for malaria control and elimination.
HOME TELEMONITORING FOR CHRONIC DISEASE MANAGEMENT: AN ECONOMIC ASSESSMENT
Authors: Paré Guy , Poba-Nzaou Placide , Sicotte Claude
Published: March 2013

Objectives: There have been very few assessments of the economics of home telemonitoring, and the quality of evidence has often been weakened by methodological flaws. This has made it difficult to compare telehomecare with traditional home care for the chronic diseases studied. This economic analysis is an attempt to address this gap in the literature.

Methods: We have analyzed the consumption of healthcare services by 95 patients with various chronic diseases over a 21-month period, that is, 12 months before, 4 months during home telemonitoring use, and over 5 months after withdraw of the technology.

Results: Our findings indicate significant benefits to the home telemonitoring program as evidenced by large reductions in number of hospitalizations, length of average hospital stay, and, to a lesser extent, number of emergency room visits. Contrary to expectations, however, the number of home visits by nurses increased both during and after the telemonitoring intervention. In terms of the financial analysis, the telehomecare program resulted in significant savings: the equivalent of over CAD1,557 per patient as calculated on an annualized basis. This represents a net gain of 41 percent as compared to traditional home care.

Conclusions: While the present economic analysis led to positive results, additional assessments should be conducted to confirm the cost-effectiveness of this mode of care delivery.
Pollution and physiological variability in gentoo penguins at two rookeries with different levels of human visitation
Authors: Barbosa Andrés , de Mas Eva , Benzal Jesús , Diaz Julia Ines , Motas Miguel , Jerez Silvia , Pertierra Luis , Benayas Javier , Justel Ana , Lauzurica Pilar , Garcia-Peña Francisco Javier , Serrano Tania
Published: March 2013

Human activity and specifically tourism has been increasing in Antarctica over the last few years. Few studies have examined the indirect effects of human visits on Antarctic penguin rookeries. This work aims to study the differences between a highly visited (Hannah Point) and a rarely visited (Devil's Point, Byers Peninsula) gentoo penguin rookery on Livingston Island. Our results suggest that potential indirect effects of human impact are observed in gentoo penguins at Hannah Point, a colony heavily visited by tourists. Penguins at Hannah Point showed a higher presence of heavy metals such as Pb and Ni and a higher number of erythrocytic nuclear abnormalities than penguins at Devil's Point. Immunological parameters showed different results depending on whether we consider the cellular response - the number of lymphocytes being higher in penguins from Hannah Point - or the humoral response - the level of immunoglobulins being higher in penguins from Devil's Point. Measurements of corticosterone levels in feathers and heterophil/lymphocyte (H/L) ratio in blood showed lower levels in the heavily visited rookery than in the rarely visited rookery. Finally, we did not detectCampylobacter jejuni, a bacteria potentially transmitted by humans in either of the populations and we did not find any difference in the prevalence ofCampylobacter laribetween the populations.
Regional weather survey on Byers Peninsula, Livingston Island, South Shetland Islands, Antarctica
Authors: Bañón Manuel , Justel Ana , Velázquez David , Quesada Antonio
Published: March 2013

In 2001 the LIMNOPOLAR Project was launched with the aim of addressing the suitability of freshwater ecosystems as useful sentinels of climate change. In this project, an automatic weather station was deployed on Byers Peninsula (Livingston Island, South Shetland Islands) near several freshwater ecosystems under research. Here the multi-year data recorded are presented and compared with meteorological time series from the observatories at the Spanish Juan Carlos I Station, Deception Island and Bellingshausen Station. Lake freezing and thawing periods and snow cover are also investigated. The main results indicate that Byers Peninsula is affected by the very cloudy and wet Antarctic maritime climate. Mean annual temperature is -2.8°C and summer mean temperatures are above freezing. The region shows moderate winds over the year and with moderate, mostly liquid precipitation during the summer. There is a significant linear relationship with meteorological records obtained from Juan Carlos I Station located on the east of Livingston Island. Correlations between meteorological data from both sites are high but with colder and much windier conditions on Byers Peninsula. Therefore, the usefulness and accuracy of meteorological records in the interpretation of ecosystem dynamics are presented.
Perceptual distinctiveness in Native American maize (Zea mays L.) landraces has practical implications
Authors: Jaradat Abdullah A.
Published: March 2013

The large variation in multifactorial and seemingly non-adaptive kernel colour traits displayed by Native American maize landraces is an evidence of recurring selection for perceptual distinctiveness. Native American farmers selected for colour traits that allowed them to distinguish between and maintain large diversity within maize landraces for traditional uses. Multivariate statistical procedures were employed to quantify the variation and interrelationships between physical traits, C:N ratio, protein content, micro- and macronutrient concentrations with kernel colour traits measured on random kernel samples of Northern flint maize landraces grown for 2 years in a common-garden experiment. The colour traits (L*, a* and b* indicating dark–light, red–green and yellow–blue colour continuum, respectively) were digitally quantified on 590 random kernels from each of 28 accessions in 11 landraces. Accessions within landraces exhibited the largest variation for all colour traits. The variation in the L*a*b*, L*a* and L*b* combinations explained significant variances in 37, 14 and 37% of 120 landrace–trait combinations, respectively; the remaining 12% were explained by L*, a* or b*. On average, 37.5% of the variation in protein content (range 19.2–64.5%) and 36.6% of the variation in the C:N ratio (range 15.7–65.0%) were explained by the combinations of colour traits in different landraces. Slightly larger average variations in K (43.7%), S (43.0%), Fe (42.2%) and P (40.8%) were accounted for by colour traits. A hierarchical and joint clustering procedure of landraces and traits was developed to facilitate the identification of large variation and the selection of single or multiple traits based on kernel colour traits with reasonable certainty.
Probing gravitation with pulsars
Authors: Kramer Michael
Published: March 2013

Radio pulsars are fascinating and extremely useful objects. Despite our on-going difficulties in understanding the details of their emission physics, they can be used as precise cosmic clocks in a wide-range of experiments – in particular for probing gravitational physics. While the reader should consult the contributions to these proceedings to learn more about this exciting field of discovering, exploiting and understanding pulsars, we will concentrate here on on the usage of pulsars as gravity labs.
The PALFA Survey: Going to great depths to find radio pulsars
Authors: Lazarus P.
Published: March 2013

The on-going PALFA survey is searching the Galactic plane (|b| < 5°, 32° < l < 77° and 168° < l < 214°) for radio pulsars at 1.4 GHz using ALFA, the 7-beam receiver installed at the Arecibo Observatory. By the end of August 2012, the PALFA survey has discovered 100 pulsars, including 17 millisecond pulsars (P < 30 ms). Many of these discoveries are among the pulsars with the largest DM/P ratios, proving that the PALFA survey is capable of probing the Galactic plane for millisecond pulsars to a much greater depth than any previous survey. This is due to the survey's high sensitivity, relatively high observing frequency, and its high time and frequency resolution. Recently the rate of discoveries has increased, due to a new more sensitive spectrometer, two updated complementary search pipelines, the development of online collaborative tools, and access to new computing resources. Looking forward, focus has shifted to the application of artificial intelligence systems to identify pulsar-like candidates, and the development of an improved full-resolution pipeline incorporating more sophisticated radio interference rejection. The new pipeline will be used in a complete second analysis of data already taken, and will be applied to future survey observations. An overview of recent developments, and highlights of exciting discoveries will be presented.
The hunt for new pulsars with the Green Bank Telescope
Authors: Lynch Ryan S.
Published: March 2013

The Green Bank Telescope (GBT) is the largest fully steerable radio telescope in the world and is one of our greatest tools for discovering and studying radio pulsars. Over the last decade, the GBT has successfully found over 100 new pulsars through large-area surveys. Here I discuss the two most recent—the GBT 350 MHz Drift-scan survey and the Green Bank North Celestial Cap survey. The primary science goal of both surveys is to find interesting individual pulsars, including young pulsars, rotating radio transients, exotic binary systems, and especially bright millisecond pulsars (MSPs) suitable for inclusion in Pulsar Timing Arrays, which are trying to directly detect gravitational waves. These two surveys have combined to discover 85 pulsars to date, among which are 14 MSPs and many unique and fascinating systems. I present highlights from these surveys and discuss future plans. I also discuss recent results from targeted GBT pulsar searches of globular clusters and Fermi sources.
Fermi-LAT searches for γ-ray pulsars
Authors: Saz Parkinson P. M. ,   for the Fermi LAT Collaboration
Published: March 2013

The Large Area Telescope (LAT) on the Fermi satellite is the first γ-ray instrument to discover pulsars directly via their γ-ray emission. Roughly one third of the 117 γ-ray pulsars detected by the LAT in its first three years were discovered in blind searches of γ-ray data and most of these are undetectable with current radio telescopes. I review some of the key LAT results and highlight the specific challenges faced in γ-ray (compared to radio) searches, most of which stem from the long, sparse data sets and the broad, energy-dependent point-spread function (PSF) of the LAT. I discuss some ongoing LAT searches for γ-ray millisecond pulsars (MSPs) and γ-ray pulsars around the Galactic Center. Finally, I outline the prospects for future γ-ray pulsar discoveries as the LAT enters its extended mission phase, including advantages of a possible modification of the LAT observing profile.
Central compact objects and their magnetic fields
Authors: Ho Wynn C. G.
Published: March 2013

Central compact objects (CCOs) are neutron stars that are found near the center of supernova remnants, and their association with supernova remnants indicates these neutron stars are young (≲ 104 yr). Here we review the observational properties of CCOs and discuss implications, especially their inferred magnetic fields. X-ray timing and spectral measurements suggest CCOs have relatively weak surface magnetic fields (~ 1010 − 1011 G). We argue that, rather than being created with intrinsically weak fields, CCOs are born with strong fields and we are only seeing a weak surface field that is transitory and evolving. This could imply that CCOs are one manifestation in a unified picture of neutron stars.
Recycling Pulsars: spins, masses and ages
Authors: Tauris T. M. , Kramer M. , Langer N.
Published: March 2013

Although the first millisecond pulsars (MSPs) were discovered 30 years ago we still do not understand all details of their formation process. Here, we present new results from Tauris, Langer & Kramer (2012) on the recycling scenario leading to radio MSPs with helium or carbon-oxygen white dwarf companions via evolution of low- and intermediate mass X-ray binaries (LMXBs, IMXBs). We discuss the location of the spin-up line in the PṖ–diagram and estimate the amount of accreted mass needed to obtain a given spin period and compare with observations. Finally, we constrain the true ages of observed recycled pulsars via calculated isochrones in the PṖ–diagram.
Constraining the nanohertz gravitational wave background with the Parkes Pulsar Timing Array
Authors: Shannon Ryan
Published: March 2013

The direct detection of gravitational waves will usher in a new era of astrophysics, enabling the study of regions of the universe opaque to electromagnetic radiation or electromagnetically quiet. An ensemble of pulsars (referred to as a pulsar timing array) provides a set of clocks distributed across the Galaxy sensitive to gravitational waves with periods on the order of five years (frequencies of many nanohertz). Plausible source of gravitational waves in this frequency band include massive black hole binaries in the throes of mergers and oscillating cosmic strings. The stochastic gravitational wave background, the sum of gravitational waves emitted throughout the universe, is the most likely signal to be detected by a pulsar timing array.

While the detection of gravitational waves will be a milestone in pulsar astronomy, a constraining limit on the strength of the gravitational wave background can be used to constrain cosmological models and early Universe physics. Here we present a new algorithm that can be used to constrain the strength of the GWB with a pulsar timing array. We then apply this technique to Parkes Pulsar Timing Array observations and place a new limit on the strength of the GWB. We conclude by discussing the astrophysical implications of this limit and the prospects for detecting gravitational waves with pulsars.
19 Years of high precision timing of the millisecond pulsar J1713+0747
Authors: Zhu Weiwei
Published: March 2013

We report the analysis of a 19-year span of timing data on PSR J1713+0747 taken by the Arecibo and Green Bank telescopes. PSR J1713+0747 is one of the best high-timing-precision pulsars monitored by the NANOGrav project for the purpose of detecting gravitational waves. The timing precision of this pulsar can be regarded as the benchmark of NANOGrav timing instruments. We show the precision improvement achieved by multi-generation instruments including the Green Bank Ultimate Pulsar Processing Instrument (GUPPI) and its counterpart in Arecibo. The new timing solution we found improves the measurement of the pulsars mass, its orbital and geometric parameters, sets new limits on alternative gravitational theories, and may provide a high-quality single pulsar gravitational wave upper limit.
Update on the European Pulsar Timing Array
Authors: Liu Kuo
Published: March 2013

The European Pulsar Timing Array (EPTA) is one the of three global Pulsar Timing Array communities, aiming to use the clock nature of pulsars to detect gravitational wave. In this talk, I will provide an introduction to the current status of EPTA pulsar observations and present an overview of the recent results. I will also give an update on the progress of the Large European Array for Pulsar (LEAP) project, which attempts to coherently combine the data from the five biggest single site radio telescopes in Europe and make an equivalently 200-metre diameter dish. The LEAP project is an ideal effort in performing high precision pulsar timing and studying characteristics of single pulses from millisecond pulsars.
Timing noise and the long-term stability of pulsar profiles
Authors: Lyne Andrew
Published: March 2013

It has recently been shown that there is a close correlation between the slowdown rates and the pulse shapes of six pulsars, and between the slowdown rates and the flux density of three others. This indicates that these phenomena are related by changes in the current flows in the pulsar magnetospheres. In this paper we review the observational status of these studies, which have now been extended to a total of 16 pulsars having correlated slowdown and pulse emission properties. The changes seem to be due to sudden switching between just two discrete magnetospheric states in the well-known processes of mode-changing and pulse nulling. We also address how widespread these phenomena are in the wider pulsar population.
Testing gravity theories in the radiative regime using pulsar timing arrays
Authors: Lee K. J.
Published: March 2013

General relativity has predicted the existence of gravitational waves (GW), which are waves of the distortions of space-time with two degrees of polarization and the propagation speed of light. Alternative theories predict more polarizations, up to a maximum of six, and possible frequency dependent propagation speed from the light speed. The polarization and dispersion properties of GWs shed light on the spin and mass information of gravitons. Although GWs have not been directly detected yet, their amplitude upper-bounds has been addressed by research using different types of detectors. For example, the amplitude upper-bounds for the stochastic background derived from pulsar timing observations have already become astrophysically interesting. The present paper reviews proposals to test the gravity theories in the radiation regime by observing GWs using pulsar timing arrays. We also present the estimation for the upper-bounds on the amplitude of alternative modes for the stochastic background of GW.
On the peculiarities in the spin-down of isolated radio pulsars
Authors: Chukwude Augustine
Published: March 2013

We investigate the spin-down behaviour of a sample of 25 radio pulsars on decadal timescales (~ 18 years) using a continuous timing data obtained over a period of at Hartebeesthoek Radio Astronomy Observatory (HartRAO). Particular attention is placed on achieving a better time resolution of both the short-term and long-term changes in pulsar spin-down using local phase-coherent measurements of the spin-down rates (). We demonstrate that the spin-down of radio pulsars is generally complicated by a superposition of processes that may or may not be related. Specifically, our results show that (i) for 7 pulsars, the observed spin-down variation is largely stochastic, characterized by random and sustained jumps in of varying amplitudes, (ii) for 9 objects, the spin-down evolution shows dominant monotonic variations in superimposed on short-term stochastic jumps in the parameter, and (iii) for the remaining 9 pulsars, the long-term spin-down evolution is non-monotonic, dominated by some systematic excursion in the measured spin-down rates.
Interstellar scattering — New diagnostics of pulsars and the ISM
Authors: Macquart Jean-Pierre
Published: March 2013

Extreme Scattering Events and pulsar secondary spectra have highlighted fundamental problems in our understanding of the dynamics of interstellar turbulence. We describe some of these problems in detail and present the theory behind the technique of speckle imaging, which offers a prospect of revealing fundamental properties of the turbulence. It also offers the prospect of resolving pulsar magnetospheres on ~ 10 nas scales.
Pilot pulsar surveys with LOFAR
Authors: Coenen Thijs
Published: March 2013

We are performing two complementary pilot pulsar surveys as part of LOFAR commissioning. The LOFAR Pilot Pulsar Survey (LPPS) is a shallow all-sky survey using an incoherent combination of LOFAR stations. The LOFAR Tied-Array Survey (LOTAS) is a deeper pilot survey using 19 simultaneous tied-array beams. These will inform a forthcoming deep survey of the entire northern hemisphere, which is expected to discover hundreds of pulsars. Here we present early results from LPPS and LOTAS, among which are two independent pulsar discoveries.
Diffusion and advection model for particle transport in young pulsar wind nebulae
Authors: Tang Xiaping , Chevalier Roger A.
Published: March 2013

The magnetohydrodynamic (MHD) model for young pulsar wind nebulae (PWN) has been successful in reproducing many features of the nebulae. The model is characterized by a termination shock (TS) between the PWN and unshocked pulsar wind. Relativistic particles are injected at the TS and follow an advective flow to the outer boundary. However, toroidal structure of well studied young PWN like the Crab Nebula, 3C 58 and G21.5-0.9 is only present in the region close to the TS. In the outer parts of the nebulae, filamentary and loop-like structure is observed. Also, the radial variation of spectral index due to synchrotron losses is smoother than expected in the MHD flow model. We find that a pure diffusion model with energy independent diffusion and a transmitting boundary can reproduce the basic data on nebular size and spectral index variation for the Crab, 3C 58, and G21.5-0.9. Energy dependent diffusion is also discussed. Power law variations of the coefficient with energy are degenerate with variation in the input particle energy distribution index in the steady state case. Monte Carlo simulations of particle transport with both diffusion and advection for the Crab nebula and 3C 58 suggest a picture in which advection dominates the inner part of the PWN where toroidal structure is clearly present. Diffusion dominates the outer part of the PWN where filamentary and loop-like structure is observed. The source of the chaotic field is uncertain, but may be related to Rayleigh-Taylor instability at the outer boundary of young nebulae and/or the kink instability of the toroidal magnetic field.
The structure of the pulsar magnetosphere via particle simulation with GRAPE
Authors: Shibata Shinpei
Published: March 2013

It is shown with a particle simulation that the outer gap can be reproduced under a few simple assumptions. The simulation includes just the first principles, namely Maxwell's equations, a relativistic equation of motion with radiation drag, and electron-positron pair creation. We also suggest that the Y-point (the open-close boundary in the equator) is likely to be a place of heating and acceleration of plasma, and therefore it would cause high-energy emission. The dead zone along the separatrix of the oppositely directed current is found in the middle latitude region, which separates the outer gap and the polar cap accelerators.
Pulsar electrodynamics revisited
Authors: Melrose D. B. , Yuen R.
Published: March 2013

The inductive electric field is unjustifiably neglected in most models for pulsar electrodynamics; it cannot be screened by the magnetospheric plasma, and it is not small in comparison with the corotation electric field. The perpendicular component of the inductive electric field implies a drift motion that is inconsistent with corotation at any angular velocity. Some implications of the inductive electric field and the associated drift motion are discussed.
Resistivity and dissipation in pulsar magnetospheres
Authors: Li Jason , Spitkovsky Anatoly , Tchekhovskoy Alexander
Published: March 2013

Current models of pulsar magnetospheres typically assume either a complete absence of plasma or abundant ideal plasma filling the magnetosphere in order to compute the field structure. The latter condition is thought to be closer to reality, but we know of a number of pulsars in which the ideal conditions break down, resulting in dissipation and high-energy emission. In this work we formulate a resistive force-free scheme that allows us to consider the effects of resistive plasma and accelerating fields on the magnetospheric structure. We run numerical simulations to construct a family of resistive solutions that smoothly bridges the gap between the vacuum and the force-free magnetosphere solutions. We further provide a self-consistent model for the spin-down of intermittent pulsars, pulsars which appear to transition between radio-loud and radio-quiet states with different spin-down rates. Finally, we present models for high-energy emission from reconnecting current sheets in Gamma-ray pulsars.
Elementary radiation patterns in pulsar profiles
Authors: Dyks Jarosław , Rudak Bronisław
Published: March 2013

Highly symmetric double features observed in averaged pulsar profiles can be interpreted as the imprint of microscopic radiation beam characteristic of radiative mechanism operating in pulsar magnetosphere. The data put strong constraints on the possible radiation patterns, excluding entire classes of mechanisms, such as those based on parallel acceleration, or those that have complicated beams. Instead, several properties of double features (such as their symmetry, depth, shape, merging rate, large polarisation degree, and the association with bifurcated emission components) are consistent with the extraordinary-mode part of the curvature radiation beam. This shows that double notches are a clear signature of the curvature radiation process. We show that even with the emission process fixed, detailed modelling of double features remains a rather sophisticated and demanding task.
Pulsar emission at the bottom end of the electromagnetic spectrum
Authors: Kondratiev Vladislav ,   the LOFAR Pulsar Working Group
Published: March 2013

Pulsars are arguably the only astrophysical sources whose emission spans the entire electromagnetic spectrum, from decameter radio wavelengths to TeV energies. The LOw Frequency ARray (LOFAR) offers the unique possibility to study pulsars over a huge fractional bandwidth in the bottom 4 octaves of the radio window, from 15–240 MHz. Here we present a LOFAR study of pulsar single pulses, focussing specifically on the bright nearby pulsar B0809+74. We show that the spectral width of bright low-frequency pulses can be as narrow as 1 MHz and scales with increasing frequency as Δ f/fc ~ 0.15, at least in the case of the PSR B0809+74. This appears to be intrinsic to the pulsar, as opposed to being due to propagation effects. If so, this behavior is consistent with predictions by the strong plasma turbulence model of pulsar radio emission. We also present other observed properties of the single pulses and discuss their relation to other single-pulse phenomena like giant pulses.
Closing remarks
Authors: Burnell Jocelyn Bell
Published: March 2013

This meeting started with a bang, with the announcement of what appears to be another ‘Lorimer burst’. Two more ‘diamond planets’, white dwarf binary companions made of crystalline carbon, quickly followed. This drama in the first session gave way to numerous interesting, surprising results. We still have not found a pulsar orbiting a black hole, but we do have the first triple system with the pulsar in the inner binary and a main sequence star forming the outer part of the binary; it may allow tests of the Equivalence Principle. Another close binary may allow checking for dipolar gravitational radiation. Work on the spin-up of millisecond pulsars is better determining the mass accreted during the spin-up and more sophisticated determination of their ages. Indications of more high mass (~2M⊙) pulsars will allow constraints to be placed on the Equation of State for a neutron star. As was remarked, ‘We keep finding cool new pulsars wherever we look!’; Duncan Lorimer predicted we would know of 4000 pulsars by 2020, a doubling of the present number.
Relativistic strange stars with anisotropy and B-parameter in pseudo spheroidal space time
Authors: Chattopadhyay P. K. , Paul B. C.
Published: March 2013

A class of compact cold stars in the presence of strange matter is obtained for a pseudo-spheroidal geometry. Considering the strange matter equation of state $p = \frac{1}{3}(\rho-4B)$ with pressure anisotropy described by Vaidya-Tikekar metric, we determine the parameter B both inside and on the surface of the star for different values of anisotropy parameter α. In the anisotropic case, we note that a stable model of a compact star may be realized.
Pulsar time scale and its future application
Authors: Chen Ding , Hobbs George , Coles William , Manchester Richard
Published: March 2013

An Ensemble Pulsar Time Scale (EPT) is derived based on the Pulsar Timing Array. It is interesting to compare the EPT with the TT terrestrial time scale, and get many new realization on the pulsar time scale and the algorithm. Some future interesting applications of the EPT are described and discussed.
Annular gap model for multi-wavelength pulsed emission from young and millisecond pulsars
Authors: Du Yuan Jie , Qiao Guo Jun
Published: March 2013

The multi-wavelength pulsed emission from young pulsars and millisecond pulsars can be well modeled with the single-pole 3-dimension annular gap and core gap model. To distinguish our single magnetic pole model from two-pole models (e.g. outer gap model and two-pole caustic model), the convincing values of the magnetic inclination angle and the viewing angle will play a key role.
Characterizing glitches and timing irregularities in pulsars and magnetars
Authors: Espinoza Cristobal , Antonopoulou Danai , Patruno Alessandro , Stappers Ben , Watts Anna
Published: March 2013

As the quantity and quality of timing data improves, we have reached the point at which the difference between timing noise and small glitches is unclear. As a consequence, the number of events reported as glitches which show unusual properties, quite different to those of giant glitches, has increased. For example, there is now a substantial population of glitches that apparently involve a decrease in spin-down rate rather than an increase. Motivated by the theoretical implications of such a result, we are conducting a detailed review of how glitches are detected and characterised. We have focused on three main questions: the observational biases affecting glitch detection; the methods used to characterise error bars on changes in spin and spin derivatives; and the physical mechanisms that could potentially explain the different populations of timing irregularities, in the light of improved characterisation. While glitches are thought to be a consequence of the internal dynamics of the star, magnetospheric processes may be responsible for other irregularities, as timing noise and peculiar glitch recoveries. We report the first results from this study, using a small sample of radio pulsars that exhibit a wide variety of glitching behaviour.
A survey of nulling pulsars using the Giant Meterwave Radio Telescope
Authors: Gajjar Vishal , Joshi Bhal Chandra , Kramer Michael
Published: March 2013

Several pulsars show sudden cessation of pulsed emission, which is known as pulsar nulling. In this paper, the nulling behaviour of 15 pulsars is presented. The nulling fraction of these pulsars, along with the degree of reduction in the pulse energy during the null phase are reported for these pulsars. A unique nulling behaviour is re- ported for PSR J1738-2330, which also showed quasi-periodic bursts. The distributions of lengths of the null and burst phases as well as the typical nulling time scales are estimated for eight strong pulsars. A comparison of the nulling time scales of four pulsars with similar nulling fraction suggests that the fraction of null pulses probably does not quantify the nulling behaviour of a pulsar in full detail. Analysis of these distributions also indicate that while the null and the burst pulses occur in groups, the transition from the null to burst phase and vice verse can be modeled by a Poisson point process.
Magnetars are super hot and super cool
Authors: Ho Wynn C. G. , Glampedakis Kostas , Andersson Nils
Published: March 2013

We examine to what extent the inferred surface temperature of magnetars in quiescence can constrain the presence of a superfluid in the neutron star core and the role of magnetic field decay in the core. By performing detailed simulations of neutron star cooling, we show that extremely strong heating from field decay in the core cannot produce the high observed surface temperatures nor delay the onset of neutron superfluidity in the core. We find that it is not possible to conclude that magnetar cores are in a non-superfluid state purely from high surface temperatures. We find that neutron superfluidity in the core occurs less than a few hundred years after neutron star formation for core fields < 1016 G. Thus all known neutron stars, including magnetars, without a core containing exotic particles, should have a core of superfluid neutrons and superconducting protons.
Population synthesis of young neutron stars
Authors: Igoshev Andrei P. , Kholtygin Alexander F.
Published: March 2013

We investigate the fortune of young neutron stars (NS) in the whole volume of the Milky Way with new code for population synthesis. We start our modeling from the birth of massive OB stars and follow their motion in the Galaxy up to the Supernova explosion. Next we integrate the equations of motion of NS in the averaged gravitational potential of the Galaxy. We estimate the mean kick velocities from a comparison the model Z and R-distributions of radio emitting NS with that for galactic NS accordingly ATNF pulsar catalog. We follow the history of the rotational velocity and the surface magnetic field of NS taking into account the significant magnetic field decay during the first million year of a neutron star's life. The derived value for the mean time of ohmic decay is 2.3ċ105 years. We model the subsample of galactic radio pulsars which can be detected with available radio telescopes, using a radio beaming model with inhomogeneous distribution of the radio emission in the cone. The distributions functions of the pulsar periods P, period derivatives Ṗ and surface magnetic fields B appear to be in a close agreement with those obtained from an ensemble of neutron stars in the ATNF catalogue.
Distribution of ionized gas density measured by differential VLBI Observations of pulsars
Authors: Kameya Osamu
Published: March 2013

Differential VLBI observations of pulsars in our Galaxy can derive trigonometric parallax of them. Distance to pulsars derived by the parallax are very important to estimate some mean density of ionized gas between pulsars and the earth using rotation measures of them. Some preliminary results of distribution of the ionized gas density in our galaxy by using previous VLBI results are shown. Possibility of VLBI observations of pulsars using VERA and the other VLBI antennas will be described.
Magnetic field evolution in magnetars
Authors: Kojima Yasufumi
Published: March 2013

Dynamics of magnetic field decay is numerically studied. For neutron stars with strong magnetic fields, the Hall drift timescale in their crust is very short, and therefore the evolution is significantly affected. The nonlinear coupling between poloidal and toroidal components of the magnetic field is studied. It is also found that the polar field at the surface is highly distorted during the Hall drift timescale. For example, polar dipole field-strength temporarily decreases not by dissipation but by advection. This fact suggests that the dipole field-strength is not sufficient to determine the border between pulsars and magnetars.
A data analysis library for gravitational wave detection
Authors: Lassus A. , van Haasteren R. , Mingarelli C. M. F. , Lee K. J. , Vecchio A.
Published: March 2013

One of the main goals of Pulsar Timing Arrays (PTAs) is the direct detection of gravitational waves (GWs). A first detection will be a major leap for astronomy and substantial effort is currently going into timing as many pulsars as possible, with the highest possible accuracy. As part of the individual PTA projects, several groups are developing data analysis methods for the final stage of a gravitational-waves search pipeline: the analysis of the timing residuals. Here we report the progress of on-going work to develop, within a Bayesian framework, a comprehensive and user friendly analysis library to search for gravitational waves in PTA data.
Relativistic Cowling approximation for fluid oscillation modes of color superconducting self-bound stars
Authors: Lugones German , Flores Cesar Vasquez
Published: March 2013

The investigation of the quasi-normal modes of oscillation of compact stars can reveal much information about their equation of state and internal structure mainly through the analysis of the expected emission of gravitational waves. In this work we study non-radial oscillation modes of strange stars consisting of color superconducting quark matter. We focus on the fundamental and pressure oscillation modes within the frame of the Cowling approximation. We discuss the observable features that may allow a differentiation among hadronic stars, strange stars, and strange stars with color superconductivity.
New observations of the Geminga pulsar at low radio frequencies
Authors: Malofeev V. M. , Malov O. I. , Logvinenko S. V. , Teplykh D. A.
Published: March 2013

New evidence for the detection of Geminga at three low frequencies is presented. The observations were carried out on two sensitive transit radio telescopes in the range 42-112 MHz. We used three new digital receivers to detect the pulses and to obtain dynamic spectra. The exact value of the dispersion measure has been calculated.
Magnetic Color-flavor-locked Stars
Authors: Paulucci Laura , Ferrer Efrain J. , de la Incera Vivian , Horvath Jorge E.
Published: March 2013

Using the solutions of the gap equations of the magnetic-color-flavor-locked (MCFL) phase of paired quark matter in a magnetic field, and taking into consideration the separation between the longitudinal and transverse pressures due to the field-induced breaking of the spatial rotational symmetry, the equation of state (EoS) of the MCFL phase is self-consistently determined. Implications for stellar models of magnetized (self-bound) strange stars and hybrid (MCFL core) stars are discussed.
Ultra-compact X-ray binaries with high luminosity: a key for a new scenario
Authors: Pavlovskii Konstantin , Ivanova Natalia
Published: March 2013

Ultra-compact X-ray binaries (UCXBs) are accreting systems with periods less than 1 hour, which qualifies them to contain a degenerate donor-companion. One would expect such systems to have the easiest theoretical explanation, compared to other kinds of X-ray binaries. Nonetheless, current theory fails to explain high mass transfer (MT) rates in three recently well observed long-period UCXBs. We find that this range of MT rates can be maintained if the donor is a remnant of an out-of-thermal-equilibrium naked core of a giant which was revealed in a very recent episode of a common envelope (CE) event.
On the environments and progenitors of supernova remnants associated with highly magnetized neutron stars
Authors: Safi-Harb S. , Kumar H. S.
Published: March 2013

The distinction between the high-magnetic field pulsars (HBPs, thought to be mainly rotation-powered) and magnetars (commonly believed to be powered by their super-strong magnetic fields) has been recently blurred with the discovery of magnetar-like activity from the HBP J1846–0258 in the SNR Kes 75. What determines the spin properties of a neutron star at birth and its manifestation as a magnetar-like or more classical pulsar is still not clear. Furthermore, although a few studies have suggested very massive progenitors for magnetars, there is currently no consensus on the progenitors of these objects. To address these questions, we examine their environments by studying or revisiting their securely associated SNRs. Our approach is to: 1) infer the mass of their progenitor stars through X-ray spectroscopic studies of the thermally emitting supernova ejecta, and 2) investigate the physical properties of their hosting SNRs and ambient conditions. We here highlight our detailed studies of two SNRs: G292.2–0.5, associated with the HBP J1119–6127, and Kes 73, associated with the AXP 1E 1841–045, and summarize the current view of the other (handful) HBP/magnetar-SNR associations.
The new magnetar Swift J1822.3–1606
Authors: Scholz P. , Ng C.-Y. , Livingstone M. A. , Kaspi V. M. , Cumming A. , Archibald R.
Published: March 2013

On 2011 July 14, a transient X-ray source, Swift J1822.3–1606, was detected by Swift BAT via its burst activities. It was subsequently identified as a new magnetar upon the detection of a pulse period of 8.4 s. Using follow-up RXTE, Swift, and Chandra observations, we have determined a spin-down rate of Ṗ ~ 3 × 10−13, implying a dipole magnetic field of ~ 5 × 1013 G, second lowest among known magnetars, although our timing solution is contaminated by timing noise. The post-outburst flux evolution is well modelled by surface cooling resulting from heat injection in the outer crust, although we cannot rule out other models. We measure an absorption column density similar to that of the open cluster M17 at 10′ away, arguing for a comparable distance of ~1.6 kpc. If confirmed, this could be the nearest known magnetar.
Model of radio emission from spherically symmetric pulsar wind nebulae
Authors: Tanaka Shuta J.
Published: March 2013

We study radio emission from pulsar wind nebulae (PWNe) considering the observed spatial structure. We assume spherical symmetry of the PWN, and model the evolution of the magnetic field and the particle energy distribution. We do not consider the synchrotron cooling of particles but consider the adiabatic cooling, because we are mostly interested in the radio emission from PWNe. The model is applied to the Crab Nebula and succeeds to reproduce the observed spatially integrated spectrum in radio with a single power-law injection. In our previous work (a one-zone model), in contrast, the integrated spectrum of the Crab Nebula is reproduced by a broken power-law injection of particles. However, the spatial structure in radio is inconsistent with observations and we need a radial velocity profile which is very different from the model by Kennel & Coroniti. Further studies of the spatial structure of PWNe are important to understand the origin of the radio emission from young PWNe.
The spectral energy distributions of isolated neutron stars in the resonant cyclotron scattering model
Authors: Tong Hao , Xu Renxin
Published: March 2013

The X-ray dim isolated neutron stars (XDINSs) are peculiar pulsar-like objects, characterized by their very well Planck-like spectrum. In studying their spectral energy distributions, the optical/UV excess is a long standing problem. Recently, Kaplan et al. (2011) have measured the optical/UV excess for all seven sources, which is understandable in the resonant cyclotron scattering (RCS) model previously addressed. The RCS model calculations show that the RCS process can account for the observed optical/UV excess for most sources. The flat spectrum of RX J2143.0+0654 may due to contribution from bremsstrahlung emission of the electron system in addition to the RCS process.
Origin of the pulsar pulse fine structure
Authors: Ulyanov O. M. , Seredkina A. A. , Shevtsova A. I.
Published: March 2013

We give a new numerical model of pulsar pulse radiation through the interstellar medium (ISM) considering the propagation effects. It explains the deficit of a scattering measure at the decameter range of frequencies that leads to the possibility of detecting the pulsar pulse fine structure. The results of numerical simulation confirm that the fine structure may be detected at low frequencies and this is qualitatively agreed with the observational data.