487 research outputs found
Magnetic Field and Displacement sensor based on Giant Magneto-impedance effect
A two-core transducer assembly using a Fe73.5Nb3Cu1Si13.5B9 ribbon to detect
a change of magnetic field is proposed and tested for displacement (linear and
angular) and current sensor. Two identical inductors, with the ribbon as core,
are a part of two series resonance network, and are in high impedance state
when excited by a small a.c field of 1MHz in absence of d.c biasing field
(Hdc). When the magnetic state of one inductor is altered by biasing field,
produced by a bar magnet or current carrying coil, an ac signal proportional to
Hdc is generated by transducer. The results for the sensitivity and linearity
with displacement (linear and angular) of a magnet and with field from the
current carrying coil are presented for two particular configurations of the
transducer. High sensitivities of voltage response as much as
12micro-volt/micro-meter and 3mV/degree have been obtained for the transducer
as a linear and angular displacement sensor respectively in the transverse
configuration of exciting a.c and biasing d.c fields.Comment: 16 pages,7 figure
Anisotropic Dependence of Giant Magneto-Impedance of Amorphous Ferromagnetic Ribbon on Biasing Field
The magneto-impedance (MI) in amorphous ribbon of nominal composition
Fe73.5Nb3Cu1Si13.5B9 has been measured at 1MHz and at room temperature for
different configurations of exciting a.c and biasing d.c. fields. A large drop
in both resistance and reactance is observed as a function of d.c magnetic
field. When the d.c and a.c fields are parallel but normal to the axis of
ribbon, smaller magnetic field is needed to reduce the impedance to its small
saturated value compared to the situation when fields are along the axis of
ribbon. Larger d.c. field is required to lower the impedance when the d.c field
acts perpendicular to the plane of the ribbon. Such anisotropy in
magneto-impedance is related to the anisotropic response of the magnetization
of ribbon. The large change of impedance is attributed to large variation of
a.c permeability on the direction and magnitude of the dc biasing field.Comment: 12 pages, 7 figures, to be published in "International Journal of
Modern Physics B
The distribution of local star formation activity as a function of galaxy stellar mass, environment and morphology
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present a detailed inventory of star formation in the local Universe, dissecting the cosmic star formation budget as a function of key variables that influence the star formation rate (SFR) of galaxies: stellar mass, local environment and morphology. We use a large homogeneous dataset from the SDSS to first study how the star-formation budget in galaxies with stellar masses greater than log(M/MSun) = 10 splits as a function of each parameter separately. We then explore how the budget behaves as a simultaneous function of these three parameters. We show that the bulk of the star formation at z < 0.075 (~65 per cent) takes place in spiral galaxies, that reside in the field, and have stellar masses between 10 < log(M/MSun) < 10.9. The ratio of the cosmic star formation budget hosted by galaxies in the field, groups and clusters is 21:3:1. Morphological ellipticals are minority contributors to local star formation. They make a measurable contribution to the star formation budget only at intermediate to high stellar masses, 10.3 < log(M/MSun) < 11.2 (where they begin to dominate by number), and typically in the field, where they contribute up to ~13 per cent of the total star-formation budget. This inventory of local star formation serves as a z~0 baseline which, when combined with similar work at high redshift, will enable us to understand the changes in SFR that have occurred over cosmic time and offers a strong constraint on models of galaxy formation.Peer reviewe
A catalogue of faint local radio AGN and the properties of their host galaxies
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present a catalogue of 2210 local ( z < 0.1) galaxies that contain faint active galactic nuclei (AGN). We select these objects by identifying galaxies that exhibit a significant excess in their radio luminosities, compared to what is expected from the observed levels of star formation activity in these systems. This is achieved by comparing the optical (spectroscopic) star formation rate (SFR) to the 1.4 GHz luminosity measured from the Faint Images of the Radio Sky at Twenty centimeters survey. The majority of the AGN identified in this study are fainter than those in previous work, such as in the Best and Heckman (2012) catalogue. We show that these faint AGN make a non-negligible contribution to the radio luminosity function at low luminosities (below 1022.5 W Hz−1), and host ∼13 per cent of the local radio luminosity budget. Their host galaxies are predominantly high stellar-mass systems (with a median stellar mass of 1011 M⊙), are found across a range of environments (but typically in denser environments than star-forming galaxies) and have early-type morphologies. This study demonstrates a general technique to identify AGN in galaxy populations where reliable optical SFRs can be extracted using spectro-photometry and where radio data are also available so that a radio excess can be measured. Our results also demonstrate that it is unsafe to infer SFRs from radio emission alone, even if bright AGN have been excluded from a sample, since there is a significant population of faint radio AGN that may contaminate the radio-derived SFRs.Peer reviewedFinal Published versio
Better age estimations using UV-optical colours: breaking the age-metallicity degeneracy
We demonstrate that the combination of GALEX UV photometry in the FUV (~1530
angstroms) and NUV (~2310 angstroms) passbands with optical photometry in the
standard U,B,V,R,I filters can efficiently break the age-metallicity
degeneracy. We estimate well-constrained ages, metallicities and their
associated errors for 42 GCs in M31, and show that the full set of
FUV,NUV,U,B,V,R,I photometry produces age estimates that are ~90 percent more
constrained and metallicity estimates that are ~60 percent more constrained
than those produced by using optical filters alone. The quality of the age
constraints is comparable or marginally better than those achieved using a
large number of spectrscopic indices.Comment: Published in MNRAS (2007), 381, L74 (doi:
10.1111/j.1745-3933.2007.00370.x
The most recent burst of Star Formation in the Massive Elliptical Galaxy NGC 1052
High-spatial resolution near-infrared (NIR) images of the central 24 x 24
arcsec^2 (~ 2 x 2 kpc^2) of the elliptical galaxy NGC 1052 reveal a total of 25
compact sources randomly distributed in the region. Fifteen of them exhibit
Halpha luminosities an order of magnitude above the estimate for an evolved
population of extreme horizontal branch stars. Their Halpha equivalent widths
and optical-to-NIR spectral energy distributions are consistent with them being
young stellar clusters aged < 7 Myr. We consider this to be the first direct
observation of spatially resolved star-forming regions in the central
kiloparsecs of an elliptical galaxy. The sizes of these regions are ~< 11 pc
and their median reddening is E(B - V) ~ 1 mag. According to previous works,
NGC 1052 may have experienced a merger event about 1 Gyr ago. On the assumption
that these clusters are spreaded with similar density over the whole galaxy,
the fraction of galaxy mass (5 x 10^{-5}) and rate of star formation (0.01
Msun/yr) involved, suggest the merger event as the possible cause for the star
formation we see today.Comment: 5 pages, 3 figures. Accepted for publication in MNRAS Letter
The UV colours of high-redshift early-type galaxies: evidence for recent star formation and stellar mass assembly over the last 8 billion years
We combine deep UBVRIzJK photometry from the Multiwavelength Survey by
Yale-Chile (MUSYC) with redshifts from the COMBO-17 survey to perform a
large-scale study of the rest-frame ultraviolet (UV) properties of 674
high-redshift (0.5<z<1) early-type galaxies, drawn from the Extended Chandra
Deep Field South (E-CDFS). Galaxy morphologies are determined through visual
inspection of Hubble Space Telescope (HST) images taken from the GEMS survey.
We harness the sensitivity of the UV to young (<1 Gyr old) stars to quantify
the recent star formation history of early-type galaxies across a range of
luminosities (-23.5 < M(V) < -18). Comparisons to simple stellar populations
forming at high redshift indicate that only ~1.1 percent of early-types in this
sample are consistent with purely passive ageing since z=2. Parametrising the
recent star formation (RSF) in terms of the mass fraction of stars less than a
Gyr old, we find that the early-type population as a whole shows a typical RSF
between 5 and 13% in the redshift range 0.5<z<1. Early-types on the UV red
sequence show RSF values less than 5% while the reddest early-types are
virtually quiescent with RSF values of ~1%. We find compelling evidence that
early-types of all luminosities form stars over the lifetime of the Universe,
although the bulk of their star formation is already complete at high redshift.
This tail-end of star formation is measurable and not negligible, with luminous
(-23<M(V)<-20.5) early-types potentially forming 10-15% of their mass since
z=1, with their less luminous (M(V)>-20.5) counterparts potentially forming
30-60 percent of their mass in the same redshift range. (abridged)Comment: Submitted to MNRA
The UV properties of E+A galaxies: constraints on feedback-driven quenching of star formation
We present the first large-scale study of E+A (post-starburst) galaxies that
incorporates photometry in the ultraviolet (UV) wavelengths. We find that the
starburst that creates the E+A galaxy typically takes place within the last Gyr
and creates a high fraction (20-60 percent) of the stellar mass in the remnant
over a short timescale (< 0.1 Gyrs). We find a tight correlation between the
luminosity of our E+A galaxies and the implied star formation rate (SFR) during
the starburst. While low-luminosity E+As (M(z) > -20) exhibit implied SFRs of
less than 50 solar masses per year, their luminous counterparts (M(z) < -22)
shows SFRs greater than 300 and as high as 2000 solar masses per year,
suggesting that luminous and ultra-luminous infrared galaxies in the
low-redshift Universe could be the progenitors of massive nearby E+A galaxies.
We perform a comprehensive study of the characteristics of the quenching that
truncates the starburst in E+A systems.We find that, for galaxies less massive
than 10^10 MSun, the quenching efficiency decreases as the galaxy mass
increases. However, for galaxies more massive than 10^10 MSun, this trend is
reversed and the quenching efficiency increases with galaxy mass. Noting that
the mass threshold at which this reversal occurs is in excellent agreement with
the mass above which AGN become significantly more abundant in nearby galaxies,
we use simple energetic arguments to show that the bimodal behaviour of the
quenching efficiency is consistent with AGN and supernovae (SN) being the
principal sources of negative feedback above and below M ~ 10^10 MSun
respectively. (abridged)Comment: MNRAS in press (accepted September 2007
Clinicopathological representation of nonmetastatic Ewing sarcoma of the scapula - a case study
Ewing sarcoma (ES) is a rare type of small cell tumor of the bone and soft tissues. About 50% of ES arise in the femur and pelvis. We present a case of ES of the scapula in a seven year old female child. Because of its similarity with other small cell tumors, the diagnosis of ES is challenging and requires a combination of methods like CT scan, MRI report, histopathological evaluation and IHC, etc. The MRI report of our case has shown a consistent 5×4 cm3 mass on the left scapula. Bone marrow aspiration and biopsy of the tumor has been further analyzed. Small, round and oval cells with densely packed nuclei and scanty cytoplasm, which are characteristic to ES were observed microscopically. A positive reaction to vimentin and CD99 and negative result for the biomarkers meant for other types of tumors, favours the diagnosis of ES. The chromosomes analyzed from the peripheral blood of the patient have shown a normal karyotype. Early diagnosis of ES is very crucial for treatment. Histopathology and IHC are indispensible tools in the diagnosis of ES
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