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Nanodielectics (A "Universal" Panacea for Solving All Electrical Insualation Problems?)
This text summarizes the keynote presentation that is based on the full-length paper of the same title. Dr. Fréchette's oral presentation should not be seen as a summary of the “Brainstorm paper” but a glance at some major accomplishments, hinrances and still remaining questions relative to nanodielectrics. Are nanodielectrics a “universal” panacea? The answer to that question is no - but they've got a lot of potential
Two Dimensional Modeling of III-V Heterojunction Gate All Around Tunnel Field Effect Transistor
Tunnel Field Effect Transistor is one of the extensively researched semiconductor devices, which has
captured attention over the conventional Metal Oxide Semiconductor Field Effect Transistor. This device,
due to its varied advantages, is considered in applications where devices are scaled down to deep submicron
level. Like MOSFETs, many geometries of TFETs have been studied and analyzed in the past few
years. This work, presents a two dimensional analytical model for a III-V Heterojunction Surrounding
Gate Tunneling Field Effect Transistor. 2-D Poisson’s equation in cylindrical coordinates has been solved
to derive the expression of Surface Potential and threshold voltage of the device. A broken gap GaSb/InAs
heterostructure has been considered in this work. Variation of potential profiles are shown with different
gate and drain biases, by varying radius of the transistor,and different gate metals. Also, variation of
threshold voltage is shown with respect to channel length and radius of the nanowire
Mid-IR period-magnitude relations for AGB stars
Asymptotic Giant Branch variables are found to obey period-luminosity
relations in the mid-IR similar to those seen at K_S (2.14 microns), even at 24
microns where emission from circumstellar dust is expected to be dominant.
Their loci in the M, logP diagrams are essentially the same for the LMC and for
NGC6522 in spite of different ages and metallicities. There is no systematic
trend of slope with wavelength. The offsets of the apparent magnitude vs. logP
relations imply a difference between the two fields of 3.8 in distance modulus.
The colours of the variables confirm that a principal period with log P > 1.75
is a necessary condition for detectable mass-loss. At the longest observed
wavelength, 24 microns, many semi-regular variables have dust shells comparable
in luminosity to those around Miras. There is a clear bifurcation in LMC
colour-magnitude diagrams involving 24 micron magnitudes.Comment: 5 pages, 4 figure
The Red Rectangle: Its Shaping Mechanism and its Source of Ultraviolet Photons
The proto-planetary Red Rectangle nebula is powered by HD 44179, a
spectroscopic binary (P = 318 d), in which a luminous post-AGB component is the
primary source of both luminosity and current mass loss. Here, we present the
results of a seven-year, eight-orbit spectroscopic monitoring program of HD
44179, designed to uncover new information about the source of the
Lyman/far-ultraviolet continuum in the system as well as the driving mechanism
for the bipolar outflow producing the current nebula. Our observations of the
H-alpha line profile around the orbital phase of superior conjunction reveal
the secondary component to be the origin of the fast (max. v~560^{-1}\sun_{max} \ge 17,0002 -
5\times10^{-5}\sun^{-1}\sun$, about 5% of the
luminosity of the entire system. (abridged)Comment: Accepted for publication in Ap
Two compact HII regions at the remote outskirts of the Magellanic Clouds
The H II regions LMC N191 and SMC N77 are among the outermost massive
star-forming regions in the Magellanic Clouds. So far, few works have dealt
with these objects despite their interesting characteristics. We aim at
studying various physical properties of these objects regarding their
morphology (in the optical and Spitzer IRAC wavelengths), ionized gas emission,
nebular chemical abundances, exciting sources, stellar content, age, presence
or absence of young stellar objects, etc. This study is based mainly on optical
ESO NTT observations, both imaging and spectroscopy, coupled with other archive
data, notably Spitzer images (IRAC 3.6, 4.5, 5.8, and 8.0 microns) and 2MASS
observations. We show the presence of two compact H II regions, a
low-excitation blob (LEB) named LMC N191A and a high-excitation blob (HEB)
named SMC N77A, and study their properties and those of their exciting massive
stars as far as spectral type and mass are concerned. We also analyze the
environmental stellar populations and determine their evolutionary stages.
Based on Spitzer IRAC data, we characterize the YSO candidates detected in the
direction of these regions. Massive star formation is going on in these young
regions with protostars of mass about 10 and 20 M_sun in the process of
formation.Comment: 14 pages, 8 figures, 6 tables; Accepted for publication in A&A. arXiv
admin note: substantial text overlap with arXiv:1102.125
Herschel Observations of a Newly Discovered UX Ori Star in the Large Magellanic Cloud
The LMC star, SSTISAGE1C J050756.44-703453.9, was first noticed during a
survey of EROS-2 lightcurves for stars with large irregular brightness
variations typical of the R Coronae Borealis (RCB) class. However, the visible
spectrum showing emission lines including the Balmer and Paschen series as well
as many Fe II lines is emphatically not that of an RCB star. This star has all
of the characteristics of a typical UX Ori star. It has a spectral type of
approximately A2 and has excited an H II region in its vicinity. However, if it
is an LMC member, then it is very luminous for a Herbig Ae/Be star. It shows
irregular drops in brightness of up to 2 mag, and displays the reddening and
"blueing" typical of this class of stars. Its spectrum, showing a combination
of emission and absorption lines, is typical of a UX Ori star that is in a
decline caused by obscuration from the circumstellar dust. SSTISAGE1C
J050756.44-703453.9 has a strong IR excess and significant emission is present
out to 500 micron. Monte Carlo radiative transfer modeling of the SED requires
that SSTISAGE1C J050756.44-703453.9 has both a dusty disk as well as a large
extended diffuse envelope to fit both the mid- and far-IR dust emission. This
star is a new member of the UX Ori subclass of the Herbig Ae/Be stars and only
the second such star to be discovered in the LMC.Comment: ApJ, in press. 9 pages, 5 figure
Testing Mass Loss in Large Magellanic Cloud Cepheids using Infrared and Optical Observations II. Predictions and Tests of the OGLE-III Fundamental-Mode Cepheids
In this article, we test the hypothesis that Cepheids have infrared excesses
due to mass loss. We fit a model using the mass-loss rate and the stellar
radius as free parameters to optical observations from the OGLE-III survey and
infrared observations from the 2MASS and SAGE data sets. The sample of Cepheids
have predicted minimum mass-loss rates ranging from zero to
, where the rates depend on the chosen dust properties. We use the
predicted radii to compute the Period-Radius relation for LMC Cepheids, and to
estimate the uncertainty caused by the presence of infrared excess for
determining angular diameters with the infrared surface brightness technique.
Finally, we calculate the linear and non-linear Period-Luminosity (P-L)
relations for the LMC Cepheids at VIJHK + IRAC wavelengths and we find that the
P-L relations are consistent with being non-linear at infrared wavelengths,
contrary to previous results.Comment: 17 pages, 12 figures, 5 tables, ApJ Accepte
The Excitation of Extended Red Emission: New Constraints on its Carrier From HST Observations of NGC 7023
The carrier of the dust-associated photoluminescence process causing the
extended red emission (ERE) in many dusty interstellar environments remains
unidentified. Several competing models are more or less able to match the
observed broad, unstructured ERE band. We now constrain the character of the
ERE carrier further by determining the wavelengths of the radiation that
initiates the ERE. Using the imaging capabilities of the Hubble Space
Telescope, we have resolved the width of narrow ERE filaments appearing on the
surfaces of externally illuminated molecular clouds in the bright reflection
nebula NGC 7023 and compared them with the depth of penetration of radiation of
known wavelengths into the same cloud surfaces. We identify photons with
wavelengths shortward of 118 nm as the source of ERE initiation, not to be
confused with ERE excitation, however. There are strong indications from the
well-studied ERE in the Red Rectangle nebula and in the high-|b| Galactic
cirrus that the photon flux with wavelengths shortward of 118 nm is too small
to actually excite the observed ERE, even with 100% quantum efficiency. We
conclude, therefore, that ERE excitation results from a two-step process. While
none of the previously proposed ERE models can match these new constraints, we
note that under interstellar conditions most polycyclic aromatic hydrocarbon
(PAH) molecules are ionized to the di-cation stage by photons with E > 10.5 eV
and that the electronic energy level structure of PAH di-cations is consistent
with fluorescence in the wavelength band of the ERE. Therefore, PAH di-cations
deserve further study as potential carriers of the ERE. (abridged)Comment: Accepted for Publication in the Ap
The Dust in Lyman Break Galaxies
We present our analysis of UV attenuation by internal dust of a large sample
(N=906 galaxies) of Lyman Break Galaxies (LBGs). Using spectral energy
distributions (SEDs) from the P\'EGASE galaxy spectral evolution model we apply
dust attenuation corrections to the G-R colors using the Witt & Gordon (2000)
models for radiative transfer in dusty galactic environments to arrive at the
UV attenuation factors. We show that the dust in the LBGs exhibit SMC-like
characteristics rather than MW-like, and that the dust geometry in these
systems is most likely to be represented by a clumpy shell configuration. We
show that the attenuation factor exhibits a pronounced dependence on the
luminosity of the LBG, a_{1600}\propto (L/L_\sun)^\alpha, where
. The exponent depends on the initial parameters
of the stellar population chosen to model the galaxies and the dust properties.
We find that the luminosity weighted average attenuation factor is likely to be
in the range from , which is consistent with the upper limits to the
star formation rate at set by the FIR background. This implies that the
current UV/optical surveys do detect the bulk of the star formation during the
epoch , but require substantial correction for internal dust
attenuation.Comment: 17 pages, 12 figures, uses AASTEX, accepted for publication in the
Astrophysical Journa
The Dust-to-Gas Ratio in the Small Magellanic Cloud Tail
The Tail region of the Small Magellanic Cloud (SMC) was imaged using the MIPS
instrument on the Spitzer Space Telescope as part of the SAGE-SMC Spitzer
Legacy. Diffuse infrared emission from dust was detected in all the MIPS bands.
The Tail gas-to-dust ratio was measured to be 1200 +/- 350 using the MIPS
observations combined with existing IRAS and HI observations. This gas-to-dust
ratio is higher than the expected 500-800 from the known Tail metallicity
indicating possible destruction of dust grains. Two cluster regions in the Tail
were resolved into multiple sources in the MIPS observations and local
gas-to-dust ratios were measured to be ~440 and ~250 suggests dust formation
and/or significant amounts of ionized gas in these regions. These results
support the interpretation that the SMC Tail is a tidal tail recently stripped
from the SMC that includes gas, dust, and young stars.Comment: 6 pages, 3 figures, ApJ Letters, in press, (version with full
resolution figures at
http://www.stsci.edu/~kgordon/papers/PS_files/sage-smc_taildust_v1.62.pdf
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