55 research outputs found
Bow Shocks from Neutron Stars: Scaling Laws and HST Observations of the Guitar Nebula
The interaction of high-velocity neutron stars with the interstellar medium
produces bow shock nebulae, where the relativistic neutron star wind is
confined by ram pressure. We present multi-wavelength observations of the
Guitar Nebula, including narrow-band H-alpha imaging with HST/WFPC2, which
resolves the head of the bow shock. The HST observations are used to fit for
the inclination of the pulsar velocity vector to the line of sight, and to
determine the combination of spindown energy loss, velocity, and ambient
density that sets the scale of the bow shock. We find that the velocity vector
is most likely in the plane of the sky. We use the Guitar Nebula and other
observed neutron star bow shocks to test scaling laws for their size and
H-alpha emission, discuss their prevalence, and present criteria for their
detectability in targeted searches. The set of H-alpha bow shocks shows
remarkable consistency, in spite of the expected variation in ambient densities
and orientations. Together, they support the assumption that a pulsar's
spindown energy losses are carried away by a relativistic wind that is
indistinguishable from being isotropic. Comparison of H-alpha bow shocks with
X-ray and nonthermal, radio-synchrotron bow shocks produced by neutron stars
indicates that the overall shape and scaling is consistent with the same
physics. It also appears that nonthermal radio emission and H-alpha emission
are mutually exclusive in the known objects and perhaps in all objects.Comment: 12 pages, 7 figures (3 degraded), submitted to ApJ; minor revisions
and updates in response to referee report. (AASTeX, includes emulateapj5 and
onecolfloat5.
Birth Kick Distributions and the Spin-Kick Correlation of Young Pulsars
Evidence from pulsar wind nebula symmetry axes and radio polarization
observations suggests that pulsar motions correlate with the spin directions.
We assemble this evidence for young isolated pulsars and show how it can be
used to quantitatively constrain birth kick scenarios. We illustrate by
computing several plausible, but idealized, models where the momentum thrust is
proportional to the neutrino cooling luminosity of the proto-neutron star. Our
kick simulations include the effects of pulsar acceleration and spin-up and our
maximum likelihood comparison with the data constrains the model parameters.
The fit to the pulsar spin and velocity measurements suggests that: i) the
anisotropic momentum required amounts to ~10% of the neutrino flux, ii) while a
pre-kick spin of the star is required, the preferred magnitude is small
10-20rad/s, so that for the best-fit models iii) the bulk of the spin is
kick-induced with ~120rad/s and iv) the models suggest that the
anisotropy emerges on a timescale ~1-3s.Comment: 37 pages, 13 figures, ApJ accepte
MOLECULAR CHARACTERIZATION OF K26 GENE OF LEISHMANIA INFANTUM, ISOLATE BY HUMAN PATIENTS FROM SICILY REGION
Human Leishmaniasis is an emerging problem in Italy and increase in the Sicily region.
In the present work, we explored the genetic polymorphism of Leishmania isolates from twenty-five cases of human
Leishmaniasis: two cases of visceral Leishmaniasis (VL) and twenty-three of cutaneous Leishmaniasis (CL). The
characterization is carried out in comparison with twenty five human isolates of leishmania and one reference strain, L.
infantum MHOM/TN/80IPT1 (MON-1). MON-1 is the most common zymodeme responsible for Leishmaniasis in Italy.
The aim of the study is to genotype Leishmania isolates from Sicily by PCR ,analyzing size polymorphism of K26 gene
to discriminate between MON-1 and non MON-1 zymodemes. K26 is a protein belonging to the Hydrofilic acylated
surface protein B (HASPB) family. It is characterized by repeated aminoacidal domains and shows polymorphisms. The
k26 polymorphism of MON-1 zymodeme is determinate in the size of 626 bp. The analysis show that all the 25 isolates
belong to the L. infantum species, in particular the product size of 626 bp is detect in six patients affected by cutaneous
Leishmaniasis. The molecular tools applied in this study can constitute a helpful support for parasite tracking and for a
better understanding of the epidemiological evolution of Leishmaniasis
The Radial Structure of SNR N103B
We report on the results from a Chandra ACIS observation of the young,
compact, supernova remnant N103B. The unprecedented spatial resolution of
Chandra reveals sub-arcsecond structure, both in the brightness and in spectral
variations. Underlying these small-scale variations is a surprisingly simple
radial structure in the equivalent widths of the strong Si and S emission
lines. We investigate these radial variations through spatially resolved
spectroscopy using a plane-parallel, non-equilibrium ionization model with
multiple components. The majority of the emission arises from components with a
temperature of 1 keV: a fully ionized hydrogen component; a high ionization
timescale (n_e*t > 10^12 s cm^-3) component containing Si, S, Ar, Ca, and Fe;
and a low ionization timescale (n_e*t ~ 10^{11} s cm^-3) O, Ne, and Mg
component. To reproduce the strong Fe Kalpha line, it is necessary to include
additional Fe in a hot (> 2 keV), low ionization (n_e*t ~ 10^10.8 s cm^-3)
component. This hot Fe may be in the form of hot Fe bubbles, formed in the
radioactive decay of clumps of 56Ni. We find no radial variation in the
ionization timescales or temperatures of the various components. Rather, the Si
and S equivalent widths increase at large radii because these lines, as well as
those of Ar and Ca, are formed in a shell occupying the outer half of the
remnant. A shell of hot Fe is located interior to this, but there is a large
region of overlap between these two shells. In the inner 30% of the remnant,
there is a core of cooler, 1 keV Fe. We find that the distribution of the
ejecta and the yields of the intermediate mass species are consistent with
model prediction for Type Ia events.Comment: 34 pages, including 7 tables and 7 figures, Accepted by Ap
Cross-sectional survey of canine leishmaniasis in pantelleria island in sicily
Dogs are the major reservoir of Leishmania infantum, the causative agent of canine visceral and cutaneous human leishmaniasis in the Mediterranean basin. Canine and human leishmaniosis are endemic in Italy, particularly in central and southern regions, including islands. Here we show a preliminary, clinical, serological and molecular study carried out in Pantelleria island during 2017. In this study, we clinically examined 136 dogs for the presence of symptoms compatible with leishmaniasis, determined the titer of anti-Leishmania antibodies, and investigated Leishmania DNA by real time PCR in blood and/or lymph node of each dog. The prevalence of disease was equal to 27% with 95% CI [21%; 32%], lower than prevalence obtained in the other Sicily islands (Lampedusa, Lipari). We observed that enlarged lymph nodes was more positivitely associated with canine leishmaniasis (CanL) than other clinical signs. The results obtained showed that in an endemic area, such as Sicily, diagnosis of CanL needs to be carried out by including an immunological, molecular clinical approach
Precision Southern Hemisphere pulsar VLBI astrometry: techniques and results for PSR J1559-4438
We describe a data reduction pipeline for VLBI astrometric observations of
pulsars, implemented using the ParselTongue AIPS interface. The pipeline
performs calibration (including ionosphere modeling), phase referencing with
proper accounting of reference source structure, amplitude corrections for
pulsar scintillation, and position fitting to yield the position, proper motion
and parallax. The optimal data weighting scheme to minimize the total error
budget of a parallax fit, and how this scheme varies with pulsar parameters
such as flux density, is also investigated. The robustness of the techniques
employed are demonstrated with the presentation of the first results from a two
year astrometry program using the Australian Long Baseline Array (LBA). The
parallax of PSR J1559-4438 is determined to be 0.384 +- 0.081 mas (1 sigma),
resulting in a distance estimate of 2600 pc which is consistent with earlier DM
and HI absorption estimates.Comment: 30 pages, 8 figures, submitted to Ap
Fitting Pulsar Wind Tori
CXO imaging has shown that equatorial tori, often with polar jets, are very
common in young pulsar wind nebulae (PWNe). These structures are interesting
both for what they reveal about the relativistic wind itself and for the
(nearly) model-independent measurement of the neutron star spin orientation
they provide. The later is a particularly valuable probe of pulsar emission
models and of neutron star physics.We describe here a procedure for fitting
simple 3-D torus models to the X-ray data which provides robust estimates of
the geometric parameters. An application to 6 PWN tori gives orientations, PWN
shock scales and post-shock wind speeds along with statistical errors. We
illustrate the use of these data by commenting on the implications for kick
physics and for high energy beaming models.Comment: 10 pages, 2 figures; to appear in the Astrophysical Journa
Proper-Motion Measurements with the VLA. II. Observations of Twenty-eight Pulsars
Using the Very Large Array, we have measured the proper motions of
twenty-eight radio pulsars. On average, the pulsars studied are fainter and
more distant than those studied in earlier work, reducing the selection biases
inherent in surveys restricted to the Solar neighborhood. The typical
measurement precision achieved is a few milliarcseconds per year, corresponding
to a few tens of kilometers per second for a pulsar a kiloparsec away. While
our results compare well with higher-precision measurements done using
very-long baseline interferometry, we find that several earlier proper motion
surveys appear to have reported overly optimistic measurement uncertainties,
most likely because of a failure to fully account for ionospheric effects. We
discuss difficulties inherent in estimating pulsar velocities from proper
motions given poorly constrained pulsar distances. Our observations favor a
distribution with 20% of pulsars in a low velocity component (sigma_1D = 99
km/s) and 80% in a high velocity component (sigma_1D = 294 km/s). Furthermore,
our sample is consistent with a scale height of pulsar birthplaces comparable
to the scale height of the massive stars that are their presumed progenitors.
No evidence is found in our data for a significant population of young pulsars
born far from the plane. We find that estimates of pulsar ages based on
kinematics agree well with the canonical spin-down age estimate, but agreement
is improved if braking indexes are drawn from a Gaussian distribution centered
at n=3 with width 0.8.Comment: 20 pages. Accepted for publication in the Astronomical Journa
Laparotomic vs laparoscopic ovariectomy: comparing the two methods. The ovariectomy in the bitch in laparoscopic era
BACKGROUND: The aim of the present work is to evaluate the effectiveness of the use of ultrasound scalpel during laparoscopic ovariectomy in the bitch.
METHODS: Two groups of 10 subjects each, of different races and ages, were compared. In the first group, ovariectomy was performed laparoscopically, using harmonic scalpel to remove ovary. In the second group surgery was performed by means of classical laparotomy.
RESULTS: Pre-operative time was similar in both groups. Total operative time, from incision to skin suture, showed significant difference between the two groups, being laparoscopy faster than laparotomy. Partial operative time for bilateral oophorectomy resulted lower using open technique, but, considering each ovary, there was no significant difference in both groups.
CONCLUSIONS: The use of harmonic scalpel to perform ovariectomy during laparoscopy is an effective time-sparing surgical approach compared to the already great practicality of laparotomy
Genetic tools discriminate strains of leishmania infantum isolated from humans and dogs in Sicily, Italy
Background Leishmaniasis is one of the most important vector-borne diseases and it represents a seri-ous world health problem affecting millions of people. High levels of Leishmania infections, affecting both humans and animals, are recognized among Italian regions. Among these, Sicily has one of the highest prevalence of Leishmania infection. Methodology/Principal Findings Seventy-eight Leishmania strains isolated from human and animal samples across Sicily, were analyzed for the polymorphic k26-gene and genotypes were assigned according to the size of the PCR products. A multilocus microsatellite typing (MLMT) approach based on the analysis of 11 independent loci was used to investigate populations structure and genetic diversity of the isolated strains. Six L. infantum reference strains were included in the analysis for comparison. Bayesian clustering analysis of microsatellite data showed that all the isolated strains clustered in two genetically distinct populations, corresponding to human and canine isolates respectively. A further subdivision was observed between the two main groups, giving a good correlation between human strains and their geographic origin, conversely canine population showed a great genetic variability diffused in the territory. Conclusions/Significance Among the 78 Leishmania isolates, K26 analysis detected 71 samples (91%) as MON-1 zymodeme, confirming it as the predominant strain in Mediterranean area and 7 human samples (9%) as non-MON-1. MLMT gives important insights into the epidemiology of leish-maniases and allows characterization of different strains to a higher resolution than possible with zymodeme typing. Two main populations presented a strong correlation respect to the different hosts, exhibiting a co-circulation of two distinct populations of L. infantum. The population found in infected humans exhibited a correlation with geographic origin. These clusters could represent a geographically restricted population of strains with the same or related genotypes. This study can contribute to an understanding of Leishmania epidemiol-ogy, including the spread of reservoirs and sand fly vectors in the different foci of infection, characterizing parasites within the different hosts
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