9,558 research outputs found
Ammonia observations in the LBV nebula G79.29+0.46. Discovery of a cold ring and some warm spots
The surroundings of Luminous Blue Variable (LBV) stars are excellent
laboratories to study the effects of their high UV radiation, powerful winds,
and strong ejection events onto the surrounding gas and dust. The LBV
G79.29+0.46 powered two concentric infrared rings which may interact with the
infrared dark cloud (IRDC) G79.3+0.3. The Effelsberg 100m telescope was used to
observe the NH_3 (1,1), (2,2) emission surrounding G79.29+0.46 and the IRDC. In
addition, we observed particular positions in the (3,3) transition toward the
strongest region of the IRDC. We report here the first coherent shell-like
structure of dense NH_3 gas associated with an evolved massive star. The shell,
two or three orders of magnitude more tenuous than the IRDC, is well traced in
both ammonia lines, and surrounds the ionized nebula. The NH_3 emission in the
IRDC is characterized by a low and uniform rotational temperature (T_rot ~ 10
K) and moderately high opacities in the (1,1) line. The rest of the observed
field is spotted by warm or hot zones (T_rot > 30 K) and characterized by
optically thin emission of the (1,1) line. The NH_3 abundances are about
10^{-8} in the IRDC, and 10^{-10}-10^{-9} elsewhere. The warm temperatures and
low abundances of NH_3 in the shell suggest that the gas is being heated and
photo-dissociated by the intense UV field of the LBV star. An outstanding
region is found to the south-west (SW) of the LBV star within the IRDC. The
NH_3 (3,3) emission at the centre of the SW region reveals two velocity
components tracing gas at temperatures > 30K. The northern edge of the SW
region agrees with the border of the ring nebula and a region of continuum
enhancement; here, the opacity of the (1,1) line and the NH_3 abundance do not
decrease as expected in a typical clump of an isolated cold dark cloud. This
strongly suggests some kind of interaction between the ring nebula and the
IRDC.Comment: 15 pages, 13 figures, accepted by A&A. Note the change of title with
respect to previous versio
Single Production in Collisions at the NLC
Single production in collisions at the NLC can be used to
probe the Majorana nature of the heavy neutrinos present in the Left-Right
Symmetric Model below the kinematic threshold for their direct production. For
colliders in the TeV range, typical cross sections of order
are obtained, depending on the specific choice of model parameters.
Backgrounds arising from Standard Model processes are shown to be small. This
analysis greatly extends the kinematic range of previous studies wherein the
production of an on-shell, like-sign pair of 's at the NLC was considered.Comment: 13pp, 3 figures (available on request), LaTex, SLAC-PUB-647
No light shining through a wall : new results from a photoregeneration experiment
Recently, axion-like particle search has received renewed interest. In
particular, several groups have started ``light shining through a wall''
experiments based on magnetic field and laser both continuous, which is very
demanding in terms of detector background. We present here the 2 limits
obtained so far with our novel set-up consisting of a pulsed magnetic field and
a pulsed laser. In particular, we have found that the axion-like particle two
photons inverse coupling constant is GeV provided that the
particle mass 1 meV. Our results definitively invalidate
the axion interpretation of the original PVLAS optical measurements with a
confidence level greater than 99.9%.Comment: Version that will appear in Physical Review Letters, Vol. 99, n. 18,
(2 Nov 2007
Electroweak precision constraints on the Lee-Wick Standard Model
We perform an analysis of the electroweak precision observables in the
Lee-Wick Standard Model. The most stringent restrictions come from the S and T
parameters that receive important tree level and one loop contributions. In
general the model predicts a large positive S and a negative T. To reproduce
the electroweak data, if all the Lee-Wick masses are of the same order, the
Lee-Wick scale is of order 5 TeV. We show that it is possible to find some
regions in the parameter space with a fermionic state as light as 2.4-3.5 TeV,
at the price of rising all the other masses to be larger than 5-8 TeV. To
obtain a light Higgs with such heavy resonances a fine-tuning of order a few
per cent, at least, is needed. We also propose a simple extension of the model
including a fourth generation of Standard Model fermions with their Lee-Wick
partners. We show that in this case it is possible to pass the electroweak
constraints with Lee-Wick fermionic masses of order 0.4-1.5 TeV and Lee-Wick
gauge masses of order 3 TeV.Comment: 24 pages, 7 figure
Use of Robotics kits for the enhancement of metacognitive skills of mathematics: a possible approach
The present study is aimed at analyzing the process of building and programming robots as a metacognitive
tool of mathematics. Quantitative data from a study performed on a sample of students attending an Italian secondary
school are described. Results showed that robotics activities may be used as a new metacognitive environment
allowing students to improve their attitude towards mathematics, and to increase their attitude to reflect on themselves
and on their own learning, and their higher-level control components, such as forecasting, planning, monitoring and
evaluation exercises and problems related to implementation
Pathological Fractures Of The Jaws Due To Cystic Lesions: A Three Case Series With A Brief Review Of The Literature
This study aims to describe pathologic fractures of the jaws due to cystic bone lesions. Their daily clinical practice findings are not very common, so their treatment can be challenging. In addition, endosseous benign lesions like a radicular, residual, solitary, aneurysmal cyst, and odontogenic keratocyst, might weaken the bone so that trauma, or usual chewing, could break it. We follow from the first clinical examination to the X-ray or CBCT examination and surgical management of our patients, reporting all procedures and results to explain our approach to these cases. We also reviewed the literature briefly to determine if our operative management is in line with the scientific community. Mandibular angle and body are common locations, while symphysis and condyle are less so. Young men are the most affected, and trauma is the most triggering event. Cyst enucleation, followed by fracture reduction and fixation, is the treatment of choice for our clinical team and the scientific community. We observe how impactful it is to approach the cavity of the cystic lesion from the fracture line as the surgical gold standar
A search for water maser emission toward obscured post-AGB star and planetary nebula candidates
Water maser emission at 22 GHz is a useful probe to study the transition
between the nearly spherical mass-loss in the AGB to a collimated one in the
post-AGB phase. In their turn, collimated jets in the post-AGB phase could
determine the shape of planetary nebulae (PNe) once photoionization starts. We
intend to find new cases of post-AGB stars and PNe with water maser emission,
including water fountains or water-maser-emitting PNe. We observed water maser
emission in a sample of 133 objects, with a significant fraction being post-AGB
and young PN candidate sources with strong obscuration. We detected this
emission in 15 of them, of which seven are reported here for the first time. We
identified three water fountain candidates: IRAS 17291-2147, with a total
velocity spread of ~96 km/s in its water maser components and two sources (IRAS
17021-3109 and IRAS 17348-2906) that show water maser emission outside the
velocity range covered by OH masers. We have also identified IRAS 17393-2727 as
a possible new water-maser-emitting PN. The detection rate is higher in
obscured objects (14%) than in those with optical counterparts (7%), consistent
with previous results. Water maser emission seems to be common in objects that
are bipolar in the near-IR (43% detection rate). The water maser spectra of
water fountain candidates like IRAS 17291-2147 show significantly less maser
components than others (e.g., IRAS 18113-2503). We speculate that most
post-AGBs may show water maser emission with wide enough velocity spread (> 100
km/s) when observed with enough sensitivity and/or for long enough periods of
time. Therefore, it may be necessary to single out a special group of "water
fountains", probably defined by their high maser luminosities. We also suggest
that the presence of both water and OH masers in a PN is a better tracer of its
youth, rather than the presence of just one of these species.Comment: To be published in Astronomy & Astrophysics. 16 pages, 1 figure
(spanning 5 pages). This version includes some minor language corrections and
fixes some errors in Table
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