789 research outputs found
The molecular gas content of the Pipe Nebula I. Direct evidence of outflow-generated turbulence in B59?
The Pipe Nebula is a molecular cloud hosting the B59 region as its only
active star-forming clump. While the particular importance of outflows in
active star forming regions is subject of debate, the quiet nature of the gas
in B59 makes it a good site to directly see the impact of protostellar feedback
on the quiescent dense gas. Using HARP at the JCMT, we mapped the B59 region
with the J=3-2 transition of 12CO to study the kinematics and energetics of the
outflows, and 13CO and C18O to study the overall dynamics of the ambient cloud,
the physical properties of the gas, and the hierarchical structure of the
region. The B59 region has a total of 30Msun of cold and quiescent material,
mostly gravitationally bound, with narrow line widths throughout. Such low
levels of turbulence in non-star-forming sites of B59 are indicative of the
intrinsic initial conditions of the cloud. On the other hand, close to the
forming protostars the impact of the outflows is observed as a localised
increase of both line widths from 0.3 to 1 km/s, and 13CO excitation
temperatures by 2-3K. The impact of the outflows is also evident in the low
column density material which shows signs of being pushed, shaped and carved by
the outflow bow shocks as they pierce their way out of the cloud. Much of this
structure is readily apparent in a dendrogram analysis of the cloud. The low
mass of B59 together with its intrinsically quiescent gas and small number of
protostars, allows the identification of specific regions where the outflows
from the embedded sources interact the dense gas. Our study suggests that
outflows are an important mechanism for injecting and sustaining supersonic
turbulence at sub-parsec size scales. We find that less than half of the
outflow energy is deposited as turbulent energy of the gas, however this
turbulent energy is sufficient to slow down the collapse of the region.Comment: Accepted for publication in A&
InfluĂȘncia do meio nutricional na produção de celulases em fermentação semi-sĂłlida do bagaço de cana-de-açĂșcar por Aspergillus niger.
Recommended from our members
Recommended Common Data Elements for International Research in Long-Term Care Homes: Exploring the Workforce and Staffing Concepts of Staff Retention and Turnover
The aim of this review is to develop a common data element for the concept of staff retention and turnover within the domain of workforce and staffing. This domain is one of four core domains identified by the WE-THRIVE (Worldwide Elements to Harmonize Research in Long-Term Care Living Environments) group in an effort to establish an international, person-centered long-term care research infrastructure. A rapid review identified different measurement methods to assess either turnover or retention at facility level or intention to leave or stay at the individual staff level. The selection of a recommended measurement was guided by the WE-THRIVE groupâs focus on capacity rather than deficits, the expected availability of internationally comparable data, and the goal to provide a short, ecologically viable measurement. We therefore recommend to measure staffâs intention to stay with a single item, at the individual staff level. This element, we argue, is an indicator of staff stability, which is important for reduced organizational cost and improved productivity, positive work environment, and better residentâstaff relationships and quality of care
The central engine of GRB 130831A and the energy breakdown of a relativistic explosion
Gamma-ray bursts (GRBs) are the most luminous explosions in the universe, yet
the nature and physical properties of their energy sources are far from
understood. Very important clues, however, can be inferred by studying the
afterglows of these events. We present optical and X-ray observations of GRB
130831A obtained by Swift, Chandra, Skynet, RATIR, Maidanak, ISON, NOT, LT and
GTC. This burst shows a steep drop in the X-ray light-curve at s
after the trigger, with a power-law decay index of . Such a rare
behaviour cannot be explained by the standard forward shock (FS) model and
indicates that the emission, up to the fast decay at s, must be of
"internal origin", produced by a dissipation process within an
ultrarelativistic outflow. We propose that the source of such an outflow, which
must produce the X-ray flux for day in the cosmological rest frame,
is a newly born magnetar or black hole. After the drop, the faint X-ray
afterglow continues with a much shallower decay. The optical emission, on the
other hand, shows no break across the X-ray steep decrease, and the late-time
decays of both the X-ray and optical are consistent. Using both the X-ray and
optical data, we show that the emission after s can be explained
well by the FS model. We model our data to derive the kinetic energy of the
ejecta and thus measure the efficiency of the central engine of a GRB with
emission of internal origin visible for a long time. Furthermore, we break down
the energy budget of this GRB into the prompt emission, the late internal
dissipation, the kinetic energy of the relativistic ejecta, and compare it with
the energy of the associated supernova, SN 2013fu.Comment: Accepted for publication by MNRAS. 21 pages, 3 figures, 8 tables.
Extra table with magnitudes in the sourc
Avoiding overfitting of multilayer perceptrons by training derivatives
Resistance to overfitting is observed for neural networks trained with
extended backpropagation algorithm. In addition to target values, its cost
function uses derivatives of those up to the order. For
common applications of neural networks, high order derivatives are not readily
available, so simpler cases are considered: training network to approximate
analytical function inside 2D and 5D domains and solving Poisson equation
inside a 2D circle. For function approximation, the cost is a sum of squared
differences between output and target as well as their derivatives with respect
to the input. Differential equations are usually solved by putting a multilayer
perceptron in place of unknown function and training its weights, so that
equation holds within some margin of error. Commonly used cost is the
equation's residual squared. Added terms are squared derivatives of said
residual with respect to the independent variables. To investigate overfitting,
the cost is minimized for points of regular grids with various spacing, and its
root mean is compared with its value on much denser test set. Fully connected
perceptrons with six hidden layers and , and
weights in total are trained with Rprop until cost changes by
less than 10% for last 1000 epochs, or when the epoch is
reached. Training the network with weights to represent simple
2D function using 10 points with 8 extra derivatives in each produces cost test
to train ratio of , whereas for classical backpropagation in comparable
conditions this ratio is
- âŠ