4,750 research outputs found
On the frequency of N2H+ and N2D+
Context : Dynamical studies of prestellar cores search for small velocity
differences between different tracers. The highest radiation frequency
precision is therefore required for each of these species. Aims : We want to
adjust the frequency of the first three rotational transitions of N2H+ and N2D+
and extrapolate to the next three transitions. Methods : N2H+ and N2D+ are
compared to NH3 the frequency of which is more accurately known and which has
the advantage to be spatially coexistent with N2H+ and N2D+ in dark cloud
cores. With lines among the narrowests, and N2H+ and NH3 emitting region among
the largests, L183 is a good candidate to compare these species. Results : A
correction of ~10 kHz for the N2H+ (J:1-0) transition has been found (~0.03
km/s) and similar corrections, from a few m/s up to ~0.05 km/s are reported for
the other transitions (N2H+ J:3-2 and N2D+ J:1-0, J:2-1, and J:3-2) compared to
previous astronomical determinations. Einstein spontaneous decay coefficients
(Aul) are included
Appropriate antimicrobial therapy in the elderly: when half-size does not fit all frail patients
n/
Perils of inappropriate antibiotic exposure in cancer patients. A call to fast-acting synergy
Using deuterated H3+ and other molecular species to understand the formation of stars and planets
The H3+ ion plays a key role in the chemistry of dense interstellar gas
clouds where stars and planets are forming. The low temperatures and high
extinctions of such clouds make direct observations of H3+ impossible, but lead
to large abundances of H2D+ and D2H+ which are very useful probes of the early
stages of star and planet formation. Maps of H2D+ and D2H+ pure rotational line
emission toward star-forming regions show that the strong deuteration of H3+ is
the result of near-complete molecular depletion of CNO-bearing molecules onto
grain surfaces, which quickly disappears as cores warm up after stars have
formed.
In the warmer parts of interstellar gas clouds, H3+ transfers its proton to
other neutrals such as CO and N2, leading to a rich ionic chemistry. The
abundances of such species are useful tracers of physical conditions such as
the radiation field and the electron fraction. Recent observations of HF line
emission toward the Orion Bar imply a high electron fraction, and we suggest
that observations of OH+ and H2O+ emission may be used to probe the electron
density in the nuclei of external galaxies.Comment: Proceedings of the H3+ centennial symposium, to be published in RSPTA
(editor: T. Oka
Universal Local symmetries and non-superposition in classical mechanics
In the Hilbert space formulation of classical mechanics (CM), pioneered by
Koopman and von Neumann (KvN), there are potentially more observables that in
the standard approach to CM. In this paper we show that actually many of those
extra observables are not invariant under a set of universal local symmetries
which appear once the KvN is extended to include the evolution of differential
forms. Because of their non-invariance, those extra observables have to be
removed. This removal makes the superposition of states in KvN, and as a
consequence also in CM, impossible
Direct evidence of dust growth in L183 from MIR light scattering
Theoretical arguments suggest that dust grains should grow in the dense cold
parts of molecular clouds. Evidence of larger grains has so far been gathered
in near/mid infrared extinction and millimeter observations. Interpreting the
data is, however, aggravated by the complex interplay of density and dust
properties (as well as temperature for thermal emission). We present new
Spitzer data of L183 in bands that are sensitive and insensitive to PAHs. The
visual extinction AV map derived in a former paper was fitted by a series of 3D
Gaussian distributions. For different dust models, we calculate the scattered
MIR radiation images of structures that agree agree with the AV map and compare
them to the Spitzer data. The Spitzer data of L183 show emission in the 3.6 and
4.5 micron bands, while the 5.8 micron band shows slight absorption. The
emission layer of stochastically heated particles should coincide with the
layer of strongest scattering of optical interstellar radiation, which is seen
as an outer surface on I band images different from the emission region seen in
the Spitzer images. Moreover, PAH emission is expected to strongly increase
from 4.5 to 5.8 micron, which is not seen. Hence, we interpret this emission to
be MIR cloudshine. Scattered light modeling when assuming interstellar medium
dust grains without growth does not reproduce flux measurable by Spitzer. In
contrast, models with grains growing with density yield images with a flux and
pattern comparable to the Spitzer images in the bands 3.6, 4.5, and 8.0 micron.Comment: 13 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Detection of interstellar H_2D^+ emission
We report the detection of the 1_{10}-1_{11} ground state transition of
ortho-H_2D^+ at 372.421 GHz in emission from the young stellar object NGC 1333
IRAS 4A. Detailed excitation models with a power-law temperature and density
structure yield a beam-averaged H_2D^+ abundance of 3 x 10^{-12} with an
uncertainty of a factor of two. The line was not detected toward W 33A, GL
2591, and NGC 2264 IRS, in the latter source at a level which is 3-8 times
lower than previous observations. The H_2D^+ data provide direct evidence in
support of low-temperature chemical models in which H_2D^+ is enhanced by the
reaction of H_3^+ and HD. The H_2D^+ enhancement toward NGC 1333 IRAS 4A is
also reflected in the high DCO^+/HCO^+ abundance ratio. Simultaneous
observations of the N_2H^+ 4-3 line show that its abundance is about 50-100
times lower in NGC 1333 IRAS 4A than in the other sources, suggesting
significant depletion of N_2. The N_2H^+ data provide independent lower limits
on the H_3^+ abundance which are consistent with the abundances derived from
H_2D^+. The corresponding limits on the H_3^+$ column density agree with recent
near-infrared absorption measurements of H_3^+ toward W 33A and GL 2591.Comment: Standard AAS LaTeX format (15 pages + 2 figures
Rendimiento de dos líneas comerciales de pollos parrilleros
p.105-109Se comparó la tasa de crecimiento de los cortes de interés comercial en pollos parrilleros de las líneas Arbor Acres y Cobb 500, faenados entre los 35 y 56 días de edad. La tasa de crecimiento de la carcasa eviscerada se relacionó con el peso de faena, mientras que el crecimiento de la grasa abdominal, pechuga, muslos, patas, piernas y alas con el peso de la carcasa eviscerada. Todos los cortes se evaluaron con músculo, hueso y piel. En las hembras, el ritmo de crecimiento de las características estudiadas, no presentó diferencias significativas (Pmenor a 0,05) debidas a la línea comercial. En los machos, no se observaron diferencias significativas (P mayor a 0,05) en el crecimiento de la pechuga, alas y grasa abdominal, en cambio presentaron diferencias el ritmo de crecimiento de la carcasa (Pmenor a 0,01), de los muslos (P menor a 0,05), de las patas (P menor a 0,05) y de las piernas (P menor a 0,01), siendo superior en la línea Cobb 500 que en Arbor Acres
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