6,307 research outputs found
Fractional Newton-Raphson Method Accelerated with Aitken's Method
The Newton-Raphson (N-R) method is characterized by the fact that generating
a divergent sequence can lead to the creation of a fractal, on the other hand
the order of the fractional derivatives seems to be closely related to the
fractal dimension, based on the above, a method was developed that makes use of
the N-R method and the fractional derivative of Riemann-Liouville (R-L) that
has been named as the Fractional Newton-Raphson (F N-R) method.
In the following work we present a way to obtain the convergence of the F N-R
method, which seems to be at least linearly convergent for the case where the
order of the derivative is different from one, a simplified way to
construct the fractional derivative and fractional integral operators of R-L is
presented, an introduction to the Aitken's method is made and it is explained
why it has the capacity to accelerate the convergence of iterative methods to
finally present the results that were obtained when implementing the Aitken's
method in F N-R method.Comment: Newton-Raphson Method, Fractional Calculus, Fractional Derivative of
Riemann-Liouville, Method of Aitken. arXiv admin note: substantial text
overlap with arXiv:1710.0763
Intermediate Resolution Near-Infrared Spectroscopy of 36 late-M Dwarfs
We present observations of 36 late-M dwarfs obtained with the KeckII/NIRSPEC
in the J-band at a resolution of \sim20,000. We have measured projected
rotational velocities, absolute radial velocities, and pseudo-equivalent widths
of atomic lines. 12 of our targets did not have previous measurements in the
literature.
For the other 24 targets, we confirm previously reported measurements. We
find that 13 stars from our sample have vsini below our measurement threshold
(12 km/s) whereas four of our targets are fast rotators (vsini > 30 km/s). As
fast rotation causes spectral features to be washed out, stars with low
projected rotational velocities are sought for radial velocity surveys.
At our intermediate spectral resolution we have confirmed the identification
of neutral atomic lines reported in Mclean et al. 2007. We also calculated
pseudo-equivalent widths (p-EW) of 12 atomic lines. Our results confirm that
the p-EW of K I lines are strongly dependent on spectral types. We observe that
the p-EW of Fe I and Mn I lines remain fairly constant with later spectral
type. We suggest that those lines are particularly suitable for deriving
metallicities for late-M dwarfs.Comment: accepted in Astronomical Journal. 30 pages, 7 tables, and 7 figure
The substellar mass function in sigma Orionis. II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects
We investigate the mass function in the substellar domain down to a few
Jupiter masses in the young sigma Orionis open cluster (3+/-2 Ma, d =
360^+70_-60 pc). We have performed a deep IJ-band search, covering an area of
790 arcmin^2 close to the cluster centre. This survey was complemented with an
infrared follow-up in the HKs- and Spitzer 3.6-8.0 mum-bands. Using
colour-magnitude diagrams, we have selected 49 candidate cluster members in the
magnitude interval 16.1 mag < I < 23.0 mag. Accounting for flux excesses at 8.0
mum and previously known spectral features of youth, 30 objects are bona fide
cluster members. Four are first identified from our optical-near infrared data.
Eleven have most probable masses below the deuterium burning limit and are
classified as planetary-mass object candidates. The slope of the substellar
mass spectrum (Delta N / Delta M = a M^-alpha) in the mass interval 0.11 Msol M
< 0.006 Msol is alpha = +0.6+/-0.2. Any opacity mass-limit, if these objects
form via fragmentation, may lie below 0.006 Msol. The frequency of sigma
Orionis brown dwarfs with circumsubstellar discs is 47+/-15 %. The continuity
in the mass function and in the frequency of discs suggests that very low-mass
stars and substellar objects, even below the deuterium-burning mass limit, may
share the same formation mechanism.Comment: Accepted for publication in A&A (12/04/2007). It has not been edited
for language ye
Implications of zoonotic and vector-borne parasites to free-roaming cats in central Spain
Cats are definitive hosts and reservoirs for several parasites, some of which are responsible for serious zoonotic diseases. We conducted a case-control study of data from a trap-neuter-return (TNR) programme (years 2014-2017) designed to examine the prevalence of zoonotic parasites in free-roaming cats living in urban areas of central Spain. In the animal population tested (nâŻ=âŻ263), we detected a 29.2% prevalence of endoparasites, including high rates of cestodes (12.9%) and Toxocara cati (11.7%). While faecal samples showed no Toxoplasma gondii oocysts, the seroprevalence of T. gondii infection was 24.2%. Antibodies to Leishmania infantum were detected in 4.8% of the animals, though all skin and blood samples analyzed were PCR negative for this parasite. Ectoparasites (ticks and fleas) were found in 4.6% of the cat population, and 10.6% of the cats were detected with Otodectes cynotis. Finally, 6.3% and 7.9% cats tested positive for feline leukaemia virus and feline immunodeficiency virus, respectively. Our study provides useful information for animal-welfare and public-health, as the parasites detected can affect native wild animals through predation, competition and disease transmission. Our detection of zoonotic parasites such as L. infantum, T. gondii, T. cati, Giardia duodenalis and several ectoparasites prompts an urgent need for health control measures in stray cats.S
Apoptosis of peritoneal leucocytes during early stages of Fasciola hepatica infections in sheep
Several immunomodulatory properties have been described in Fasciola hepatica infections. Apoptosis has been shown to be an effective mechanism to avoid the immune response in helminth infections. The aim of the present work was to study apoptosis in peritoneal leucocytes of sheep experimentally infected with F. hepatica during the early stages of infection. Five groups (n = 5) of sheep were used. Groups 2â5 were orally infected with 200 metacercariae (mc) and sacrificed at 1, 3, 9 and 18 days post-infection (dpi), respectively. Group 1 was used as the uninfected control (UC). Apoptosis was detected using three different methods 1) immunocytochemistry (ICC) with a polyclonal antibody anti-active caspase-3; 2) an annexin V flow cytometry assay using the Annexin V-FITC/propidium iodide (PI); and 3) transmission electron microscopy (TEM). The differential leucocyte count revealed that the majority of peritoneal granulocytes were eosinophils, which increased significantly at 9 and 18 dpi with respect to the uninfected controls. The ICC study revealed that the percentage of caspase-3+ apoptotic peritoneal leucocytes increased significantly from 3 dpi onwards with respect to the uninfected controls. The flow cytometry annexin V assay detected a very significant (P < 0.001) increase of apoptotic peritoneal macrophages, lymphocytes and granulocytes, which remained higher than in the UC until 18 dpi. Transmission electron microscopy studies also confirmed the presence of apoptosis in peritoneal eosinophils at 18 dpi. This is the first report of apoptosis induced by F. hepatica in the peritoneal leucocytes of sheep in vivo. The results of this work suggest the importance of apoptosis induction for the survival of the juvenile parasites in the peritoneal migratory stages of infection.This work was supported by EU grants (H2020-635408-PARAGONE) and the Spanish Ministry of Science grant AGL2015-67023-C2-1-R. The TEM studies were carried out by the Central Research Services (SCAI) of the University of CĂłrdobaAccepted manuscriptVeterinari
Infrared and kinematic properties of the substellar object G 196-3B
We report unusual near- and mid-infrared photometric properties of G 196-3 B,
the young substellar companion at 16 arcsec from the active M2.5-type star G
196-3 A, using data taken with the IRAC and MIPS instruments onboard Spitzer. G
196-3 B shows markedly redder colors at all wavelengths from 1.6 up to 24
micron than expected for its spectral type, which is determined at L3 from
optical and near-infrared spectra. We discuss various physical scenarios to
account for its reddish nature, and conclude that a low-gravity atmosphere with
enshrouded upper atmospheric layers and/or a warm dusty disk/envelope provides
the most likely explanations, the two of them consistent with an age in the
interval 20-300 Myr. We also present new and accurate separate proper motion
measurements for G 196-3 A and B confirming that both objects are
gravitationally linked and share the same motion within a few mas/yr. After
integration of the combined spectrophotometric spectral energy distributions,
we obtain that the difference in the bolometric magnitudes of G 196-3 A and B
is 6.15 +/- 0.10 mag. Kinematic consideration of the Galactic space motions of
the system for distances in the interval 15-30 pc suggests that the pair is a
likely member of the Local Association, and that it lay near the past positions
of young star clusters like alpha Persei less than 85 Myr ago, where the binary
might have originated. At these young ages, the mass of G 196-3 B would be in
the range 12-25 Mjup, close to the frontier between planets and brown dwarfs.Comment: Accepted for publication in ApJ
Proper motions of field L and T dwarfs -II
By using images taken with WFCAM on UKIRT and SofI on the NTT and combining
them with 2MASS we have measured proper motions for 126 L and T dwarfs in the
dwarf archive. Two of these L dwarfs appear to have M dwarf common proper
motion companions, and 2 also appear to be high velocity dwarfs, indicating
possible membership of the thick disc. We have also compared the motion of
these 126 objects to that of numerous moving groups, and have identified new
members of the Hyades, Ursa Major and Pleiades moving groups. These new
objects, as well as those identified in Jameson et al. (2008) have allowed us
to refine the L dwarf sequence for Ursa Major that was defined by Jameson et
al. (2008).Comment: Accepted for publication in MNRAS. 10 pages, 3 figure
The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey
Context. Thanks to recent and ongoing large scale surveys, hundreds of brown
dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf
Survey is a wide-field survey for cool brown dwarfs conducted with the MegaCam
camera on the Canada-France-Hawaii Telescope telescope. Aims. Our objectives
are to find ultracool brown dwarfs and to constrain the field brown-dwarf
luminosity function and the mass function from a large and homogeneous sample
of L and T dwarfs. Methods. We identify candidates in CFHT/MegaCam i' and z'
images and follow them up with pointed near infrared (NIR) imaging on several
telescopes. Halfway through our survey we found ~50 T dwarfs and ~170 L or
ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical
ultracool dwarfs i' - z' colours, found in 780 square degrees. Results. We have
currently completed the NIR follow-up on a large part of the survey for all
candidates from mid-L dwarfs down to the latest T dwarfs known with utracool
dwarfs' colours. This allows us to draw on a complete and well defined sample
of 102 ultracool dwarfs to investigate the luminosity function and space
density of field dwarfs. Conclusions. We found the density of late L5 to T0
dwarfs to be 2.0pm0.8 x 10-3 objects pc-3, the density of T0.5 to T5.5 dwarfs
to be 1.4pm0.3 x 10-3 objects pc-3, and the density of T6 to T8 dwarfs to be
5.3pm3.1 x 10-3 objects pc-3 . We found that these results agree better with a
flat substellar mass function. Three latest dwarfs at the boundary between T
and Y dwarfs give the high density 8.3p9.0m5.1 x 10-3 objects pc-3. Although
the uncertainties are very large this suggests that many brown dwarfs should be
found in this late spectral type range, as expected from the cooling of brown
dwarfs, whatever their mass, down to very low temperature.Comment: Accepted for publication in A&
- âŠ