389 research outputs found
Slotted Microstrip Patch Antenna: A Way to Improve the Performance of Microstrip Patch Antenna
Now a days, In wireless communication the most challenging task is to design antennas with light weight , low cost and better performance. Microstrip antennas are widely used antennas because of it’s several advantages like compact size, low cost and easy to fabricate. But Microstrip antennas have also several limitations of low gain and low bandwidth. This paper describes the performance improvement technique of Microstrip antennas, which contains design rule of radiating patch, proper feed position and loading slot on patch
Spectropolarimetry of Type II supernovae (II) Intrinsic supernova polarization and its relations with the photometric/spectroscopic properties
The explosion processes of supernovae (SNe) are imprinted in their explosion
geometries. Here, we study the intrinsic polarization of 15 hydrogen-rich
core-collapse SNe and explore the relation with the photometric and
spectroscopic properties. Our sample shows diverse properties of the continuum
polarization. The polarization of most SNe has a low degree at early phases but
shows a sudden rise to \% degree at certain points during the
photospheric phase as well as a slow decline during the tail phase, with a
constant polarization angle. The variation in the timing of peak polarisation
values implies diversity in the explosion geometry: some SNe have aspherical
structures only in their helium cores, while in other SNe these reach out to a
significant part of the outer hydrogen envelope with a common axis from the
helium core to the hydrogen envelope. Other SNe show high polarization from
early phases and a change of the polarization angle around the middle of the
photospheric phase. This implies that the ejecta are significantly aspherical
to the outermost layer and have multi-directional aspherical structures.
Exceptionally, the Type~IIL SN~2017ahn shows low polarization at both the
photospheric and tail phases. Our results show that the timing of the
polarization rise in Type~IIP SNe is likely correlated with their brightness,
velocity and the amount of radioactive Ni produced: brighter SNe with faster
ejecta velocity and a larger Ni mass have more extended-aspherical
explosion geometries. In particular, there is a clear correlation between the
timing of the polarization rise and the explosion energy, that is, the
explosion asphericity is proportional to the explosion energy. This implies
that the development of a global aspherical structure, e.g., a jet, might be
the key to realising an energetic SN in the mechanism of SN explosions.Comment: 27 pages, 30 figure
Signature of Electron Capture in Iron-Rich Ejecta of SN 2003du
Late-time near-infrared and optical spectra are presented for the
normal-bright SN2003du. At about 300 days after the explosion, the emission
profiles of well isolated [FeII] lines (in particular that of the strong
1.644mu feature) trace out the global kinematic distribution of radioactive
material in the expanding. In SN2003du, the 1.644 mu [FeII] line shows a
flat-topped, profile, indicative of a thick but hollow-centered expanding
shell, rather than a strongly-peaked profile that would be expected from a
``center-filled'' distribution.Based on detailed models for exploding
Chandrasekhar mass white dwarfs, we show that the feature is consistent with
spherical explosion models.Our model predicts central region of non-radioactive
electron-capture elements up to 2500--3000km/s as a consequence of burning
under high density, and an extended region of 56Ni up to 9,000--10,000km/s.
Furthermore our analysis indicates that the 1.644mu [FeII] profile is not
consistent with strong mixing between the regions of electron- capture isotopes
and the 56Ni layers as is predicted by detailed 3D models for nuclear
deflagration fronts. We discuss the possibility that the flat-topped profile
could be produced as a result of an infrared catastrophe and conclude that such
an explanation is unlikely. We put our results in context to other SNeIa and
briefly discuss the implications of our result for the use of SNe Ia as
cosmological standard candles.Comment: 12 pages + 8 figures, ApJ (in press, Dec. 20, 2004) For high
resolution figures send E-mail to [email protected]
The fastest unbound star in our Galaxy ejected by a thermonuclear supernova
Hypervelocity stars (HVS) travel with velocities so high, that they exceed
the escape velocity of the Galaxy. Several acceleration mechanisms have been
discussed. Only one HVS (US 708, HVS 2) is a compact helium star. Here we
present a spectroscopic and kinematic analysis of US\,708. Travelling with a
velocity of , it is the fastest unbound star in our
Galaxy. In reconstructing its trajectory, the Galactic center becomes very
unlikely as an origin, which is hardly consistent with the most favored
ejection mechanism for the other HVS. Furthermore, we discovered US\,708 to be
a fast rotator. According to our binary evolution model it was spun-up by tidal
interaction in a close binary and is likely to be the ejected donor remnant of
a thermonuclear supernova.Comment: 16 pages report, 20 pages supplementary material
Hearing Loss Prevents the Maturation of GABAergic Transmission in the Auditory Cortex
Inhibitory neurotransmission is a critical determinant of neuronal network gain and dynamic range, suggesting that network properties are shaped by activity during development. A previous study demonstrated that sensorineural hearing loss (SNHL) in gerbils leads to smaller inhibitory potentials in L2/3 pyramidal neurons in the thalamorecipient auditory cortex, ACx. Here, we explored the mechanisms that account for proper maturation of γ-amino butyric acid (GABA)ergic transmission. SNHL was induced at postnatal day (P) 10, and whole-cell voltage-clamp recordings were obtained from layer 2/3 pyramidal neurons in thalamocortical slices at P16–19. SNHL led to an increase in the frequency of GABAzine-sensitive (antagonist) spontaneous (s) and miniature (m) inhibitory postsynaptic currents (IPSCs), accompanied by diminished amplitudes and longer durations. Consistent with this, the amplitudes of minimum-evoked IPSCs were also reduced while their durations were longer. The α1- and β2/3 subunit–specific agonists zolpidem and loreclezole increased control but not SNHL sIPSC durations. To test whether SNHL affected the maturation of GABAergic transmission, sIPSCs were recorded at P10. These sIPSCs resembled the long SNHL sIPSCs. Furthermore, zolpidem and loreclezole were ineffective in increasing their durations. Together, these data strongly suggest that the presynaptic release properties and expression of key postsynaptic GABAA receptor subunits are coregulated by hearing
Observations of the GRB afterglow ATLAS17aeu and its possible association with GW170104
We report the discovery and multi-wavelength data analysis of the peculiar
optical transient, ATLAS17aeu. This transient was identified in the skymap of
the LIGO gravitational wave event GW170104 by our ATLAS and Pan-STARRS
coverage. ATLAS17aeu was discovered 23.1hrs after GW170104 and rapidly faded
over the next 3 nights, with a spectrum revealing a blue featureless continuum.
The transient was also detected as a fading x-ray source by Swift and in the
radio at 6 and 15 GHz. A gamma ray burst GRB170105A was detected by 3
satellites 19.04hrs after GW170104 and 4.10hrs before our first optical
detection. We analyse the multi-wavelength fluxes in the context of the known
GRB population and discuss the observed sky rates of GRBs and their afterglows.
We find it statistically likely that ATLAS17aeu is an afterglow associated with
GRB170105A, with a chance coincidence ruled out at the 99\% confidence or
2.6. A long, soft GRB within a redshift range of would be consistent with all the observed multi-wavelength data. The
Poisson probability of a chance occurrence of GW170104 and ATLAS17aeu is
. This is the probability of a chance coincidence in 2D sky location
and in time. These observations indicate that ATLAS17aeu is plausibly a normal
GRB afterglow at significantly higher redshift than the distance constraint for
GW170104 and therefore a chance coincidence. However if a redshift of the faint
host were to place it within the GW170104 distance range, then physical
association with GW170104 should be considered.Comment: 16 pages, 6 figures, accepted to Ap
Clinical and demographic factors associated with change and maintenance of disease severity in a large registry of patients with rheumatoid arthritis
BACKGROUND: We examined models to predict disease activity transitions from moderate to low or severe and associated factors in patients with rheumatoid arthritis (RA).
METHODS: Data from RA patients enrolled in the Corrona registry (October 2001 to August 2014) were analyzed. Clinical Disease Activity Index (CDAI) definitions were used for low ( \u3c /=10), moderate ( \u3e 10 and \u3c /=22), and severe ( \u3e 22) disease activity states. A Markov model for repeated measures allowing for covariate dependence was used to model transitions between three (low, moderate, severe) states and estimate population transition probabilities. Mean sojourn times were calculated to compare length of time in particular states. Logistic regression models were used to examine impacts of covariates (time between visits, chronological year, disease duration, age) on disease states.
RESULTS: Data from 29,853 patients (251,375 visits) and a sub-cohort of 9812 patients (46,534 visits) with regular visits (every 3-9 months) were analyzed. The probability of moving from moderate to low or severe disease by next visit was 47% and 18%, respectively. Patients stayed in moderate disease for mean 4.25 months (95% confidence interval: 4.18-4.32). Transition probabilities showed 20% of patients with low disease activity moved to moderate or severe disease within 6 months; \u3e 35% of patients with moderate disease remained in moderate disease after 6 months. Results were similar for the regular-visit sub-cohort. Significant interactions with prior disease state were seen with chronological year and disease duration.
CONCLUSION: A substantial proportion of patients remain in moderate disease, emphasizing the need for treat-to-target strategies for RA patients
SN 2009kf : a UV bright type IIP supernova discovered with Pan-STARRS 1 and GALEX
We present photometric and spectroscopic observations of a luminous type IIP
Supernova 2009kf discovered by the Pan-STARRS 1 (PS1) survey and detected also
by GALEX. The SN shows a plateau in its optical and bolometric light curves,
lasting approximately 70 days in the rest frame, with absolute magnitude of M_V
= -18.4 mag. The P-Cygni profiles of hydrogen indicate expansion velocities of
9000km/s at 61 days after discovery which is extremely high for a type IIP SN.
SN 2009kf is also remarkably bright in the near-ultraviolet (NUV) and shows a
slow evolution 10-20 days after optical discovery. The NUV and optical
luminosity at these epochs can be modelled with a black-body with a hot
effective temperature (T ~16,000 K) and a large radius (R ~1x10^{15} cm). The
bright bolometric and NUV luminosity, the lightcurve peak and plateau duration,
the high velocities and temperatures suggest that 2009kf is a type IIP SN
powered by a larger than normal explosion energy. Recently discovered high-z
SNe (0.7 < z < 2.3) have been assumed to be IIn SNe, with the bright UV
luminosities due to the interaction of SN ejecta with a dense circumstellar
medium (CSM). UV bright SNe similar to SN 2009kf could also account for these
high-z events, and its absolute magnitude M_NUV = -21.5 +/- 0.5 mag suggests
such SNe could be discovered out to z ~2.5 in the PS1 survey.Comment: Accepted for publication in APJ
A Study of the Type II-P Supernova 2003gd in M74
We present photometric and spectroscopic data of the type II-P supernova
2003gd, which was discovered in M74 close to the end of its plateau phase. SN
2003gd is the first type II supernova to have a directly confirmed red
supergiant progenitor. We compare SN 2003gd with SN 1999em, a similar type II-P
supernova, and estimate an explosion date of 18th March 2003. We determine a
reddening towards the supernova of E(B-V) = 0.14+/-0.06, using three different
methods. We also calculate three new distances to M74 of 9.6+/-2.8 Mpc,
7.7+/-1.7 Mpc and 9.6+/-2.2 Mpc. The former was estimated using the
Standardised Candle Method (SCM), for type II supernovae, and the latter two
using the Brightest Supergiants Method (BSM). When combined with existing
kinematic and BSM distance estimates, we derive a mean value of 9.3+/-1.8 Mpc.
SN 2003gd was found to have a lower tail luminosity compared to other
``normal'' type II-P SNe bringing into question the nature of this supernova.
We present a discussion concluding that this is a ``normal'' type II-P
supernova which is consistent with the observed progenitor mass of 8(+4/-2) Mo.Comment: 23 pages, 24 figures to appear in MNRA
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