2,894 research outputs found
Cooling Strategies for Greenhouses in Summer: Control of Fogging by Pulse Width Modulation
The possibilities for improving the control of greenhouse fogging systems, were studied by comparing several combinations of ventilation cooling techniques, shade screening and low-pressure fogging. The study was divided into three parts: experiments, modelling and simulations. In the first part of the paper, ten combinations of five cooling techniques were tested during the summers of 2002 and 2003 in a 132m2 greenhouse with a steel structure and a single-layer methacrylate cover located in Madrid, Spain. An analysis of variance of the climatic parameters was carried out to determine which combinations produced significant differences in inside temperature or relative humidity. Comparing the values for the inside to outside temperature difference, the combination of a shade screen and above-screen fogging achieved a difference in temperature almost the same as that for under-screen fogging, but the relative humidity was significantly lower. In the second part of the study a dynamic model was developed (2002) and validated (2003). The mean absolute error obtained for inside temperature was similar in the fit and the validation and it was less than 1.5 1C in both cases. The model was used to simulate the inside air temperature for a fog system working without shading, and above and under a shade screen. Control algorithms were developed for reducing system water consumption. In the three cases a simple on/off control with a fixed fogging cycle was compared with a pulse width modulation (PWM) strategy, in which the duration of the fogging pulse was increased as a function of inside temperature. The strategies with PWM applied to the fog system were able to reduce water consumption by 8â15% with respect to the strategies with a fixed fogging cycle
The Mass Function of Newly Formed Stars (Review)
The topic of the stellar "original mass function" has a nearly 50 year
history,dating to the publication in 1955 of Salpeter's seminal paper. In this
review I discuss the many more recent results that have emerged on the initial
mass function (IMF), as it is now called, from studies over the last decade of
resolved populations in star forming regions and young open clusters.Comment: 9 pages, 1 figure; to appear in "The Dense Instellar Medium in
Galaxies -- 4'th Cologne-Bonn-Zermatt-Symposium" editted by S. Pfalzner, C.
Kramer, C. Straubmeier and A. Heithausen, Springer-Verlag (2004
Initial fixation placement in face images is driven by top-down guidance
The eyes are often inspected first and for longer period during face exploration. To examine whether this saliency of the eye region at the early stage of face inspection is attributed to its local structure properties or to the knowledge of its essence in facial communication, in this study we investigated the pattern of eye movements produced by rhesus monkeys (Macaca mulatta) as they free viewed images of monkey faces. Eye positions were recorded accurately using implanted eye coils, while images of original faces, faces with scrambled eyes, and scrambled faces except for the eyes were presented on a computer screen. The eye region in the scrambled faces attracted the same proportion of viewing time and fixations as it did in the original faces, even the scrambled eyes attracted substantial proportion of viewing time and fixations. Furthermore, the monkeys often made the first saccade towards to the location of the eyes regardless of image content. Our results suggest that the initial fixation placement in faces is driven predominantly by âtop-downâ or internal factors, such as the prior knowledge of the location of âeyesâ within the context of a face
Lithium abundances along the RGB: FLAMES-GIRAFFE spectra of a large sample of low-mass Bulge stars
Context: A small number of K-type giants on the red giant branch (RGB) is
known to be very rich in lithium (Li). This fact is not accounted for by
standard stellar evolution theory. The exact phase and mechanism of Li
enrichment is still a matter of debate. Aims: Our goal is to probe the
abundance of Li along the RGB, from its base to the tip, to confine Li-rich
phases that are supposed to occur on the RGB. Methods: For this end, we
obtained medium-resolution spectra with the FLAMES spectrograph at the VLT in
GIRAFFE mode for a large sample of 401 low-mass RGB stars located in the
Galactic bulge. The Li abundance was measured in the stars with a detectable Li
670.8 nm line by means of spectral synthesis with COMARCS model atmospheres. A
new 2MASS (J-K) - Teff calibration from COMARCS models is presented in the
Appendix. Results: Thirty-one stars with a detectable Li line were identified,
three of which are Li-rich according to the usual criterion (). The stars are distributed all along the RGB, not concentrated in
any particular phase of the red giant evolution (e.g. the luminosity bump or
the red clump). The three Li-rich stars are clearly brighter than the
luminosity bump and red clump, and do not show any signs of enhanced mass loss.
Conclusions: We conclude that the Li enrichment mechanism cannot be restricted
to a clearly defined phase of the RGB evolution of low-mass stars
(M\sim1M_{\sun}), contrary to earlier suggestions from disk field stars.Comment: 6 pages (14 with appendix), 5 figures (1 in appendix), accepted for
publication in A&
Dynamical Evolution of Young Embedded Clusters: A Parameter Space Survey
This paper investigates the dynamical evolution of embedded stellar clusters
from the protocluster stage, through the embedded star-forming phase, and out
to ages of 10 Myr -- after the gas has been removed from the cluster. The
relevant dynamical properties of young stellar clusters are explored over a
wide range of possible star formation environments using N-body simulations.
Many realizations of equivalent initial conditions are used to produce robust
statistical descriptions of cluster evolution including the cluster bound
fraction, radial probability distributions, as well as the distributions of
close encounter distances and velocities. These cluster properties are
presented as a function of parameters describing the initial configuration of
the cluster, including the initial cluster membership N, initial stellar
velocities, cluster radii, star formation efficiency, embedding gas dispersal
time, and the degree of primordial mass segregation. The results of this
parameter space survey, which includes about 25,000 simulations, provide a
statistical description of cluster evolution as a function of the initial
conditions. We also present a compilation of the FUV radiation fields provided
by these same cluster environments. The output distributions from this study
can be combined with other calculations, such as disk photoevaporation models
and planetary scattering cross sections, to ascertain the effects of the
cluster environment on the processes involved in planet formation.Comment: 65 pages including 20 figures, accepted to ApJ Supplemen
Peer Connect for African American breast cancer survivors and caregivers: a train-the-trainer approach for peer support
Racial disparities in breast cancer survivorship are a major concern nationally. How survivors cope with cancer and re-frame their lives is a critical part of survivorship. Community-academic research partnerships may facilitate access to much-needed psychosocial support for African American survivors and caregivers in rural areas, but drivers of successful intervention implementation are not well understood. The purpose of this study was to describe the training and evaluation of Community Coaches and Guides (i.e., peer supporters) using the Peer Connect program for African American breast cancer survivors and caregivers. Community engagement strategies were used to implement the training component of Peer Connect, an evidence-based program grounded in the Diffusion of Innovation Theory utilizing motivational interviewing techniques (MI) and a "train-the-trainer" model. Quantitative and qualitative methods examined implementation outcomes of feasibility, MI fidelity, and acceptability-precursor outcomes that must be achieved before examining intervention impact vis-Ă -vis changes in support care. Training was feasible to implement and replicable by the trained Community Coaches. Beyond feasibility and replicability, success was modest regarding MI fidelity. Benefits (e.g., serving as role models and having safe sources of support) and lessons learned (e.g., need for additional quality control) were identified as both facilitators and barriers to implementation and as factors that could impact the effectiveness of community-engaged programs to improve survivorship outcomes. Peer Connect, like other programs that employ community-engagement strategies, holds promise to meet the psychosocial support needs of diverse rural cancer survivor populations
Dynamically Driven Evolution of the Interstellar Medium in M51
We report the highest-fidelity observations of the spiral galaxy M51 in CO
emission, revealing the evolution of giant molecular clouds (GMCs) vis-a-vis
the large-scale galactic structure and dynamics. The most massive GMCs
(so-called GMAs) are first assembled and then broken up as the gas flow through
the spiral arms. The GMAs and their H2 molecules are not fully dissociated into
atomic gas as predicted in stellar feedback scenarios, but are fragmented into
smaller GMCs upon leaving the spiral arms. The remnants of GMAs are detected as
the chains of GMCs that emerge from the spiral arms into interarm regions. The
kinematic shear within the spiral arms is sufficient to unbind the GMAs against
self-gravity. We conclude that the evolution of GMCs is driven by large-scale
galactic dynamics --their coagulation into GMAs is due to spiral arm streaming
motions upon entering the arms, followed by fragmentation due to shear as they
leave the arms on the downstream side. In M51, the majority of the gas remains
molecular from arm entry through the inter-arm region and into the next spiral
arm passage.Comment: 6 pages, including 3 figures. Accepted, ApJ
Dynamically Driven Evolution of the Interstellar Medium in M51
Massive star formation occurs in giant molecular clouds (GMCs); an understanding of the evolution of GMCs is a prerequisite to develop theories of star formation and galaxy evolution. We report the highest-fidelity observations of the grand-design spiral galaxy M51 in carbon monoxide (CO) emission, revealing the evolution of GMCs vis-a-vis the large-scale galactic structure and dynamics. The most massive GMCs (giant molecular associations (GMAs)) are first assembled and then broken up as the gas flow through the spiral arms. The GMAs and their H_2 molecules are not fully dissociated into atomic gas as predicted in stellar feedback scenarios, but are fragmented into smaller GMCs upon leaving the spiral arms. The remnants of GMAs are detected as the chains of GMCs that emerge from the spiral arms into interarm regions. The kinematic shear within the spiral arms is sufficient to unbind the GMAs against self-gravity. We conclude that the evolution of GMCs is driven by large-scale galactic dynamicsâtheir coagulation into GMAs is due to spiral arm streaming motions upon entering the arms, followed by fragmentation due to shear as they leave the arms on the downstream side. In M51, the majority of the gas remains molecular from arm entry through the interarm region and into the next spiral arm passage
Correlation between technetium and lithium in a sample of oxygen-rich AGB variables
The aims of this paper are: 1) to revisit the Tc content of a sample of
oxygen-rich asymptotic giant branch (AGB) variables and 2) to increase the
number of such stars for which the Li abundance has been measured to provide
constraints on theoretical models of extra-mixing processes. To this end, we
analysed high-resolution spectra of 18 sample stars for the presence of
absorption lines of Tc and Li. The abundance of the latter was determined by
comparing the observed spectra to hydrostatic MARCS model spectra. Bolometric
magnitudes were established from near-IR photometry and pulsation periods. We
reclassify the star V441 Cyg as Tc-rich, and the unusual Mira star R Hya, as
well as W Eri, as Tc-poor. The abundance of Li, or an upper limit to it, was
determined for all of the sample stars. In all stars with Tc we also detected
Li. Most of them have a Li content slightly below the solar photospheric value,
except for V441 Cyg, which has ~1000 times the solar abundance. We also found
that, similar to Tc, a lower luminosity limit seems to exist for the presence
of Li. We conclude that the higher Li abundance found in the cooler and higher
luminosity objects could stem from a Li production mechanism operating on the
AGB. The stellar mass might have a crucial influence on this (extra-mixing)
production mechanism. It was speculated that the declining pulsation period of
R Hya is caused by a recent thermal pulse (TP). While not detecting Tc does not
rule out a TP, it indicates that the TPs are not strong enough to drive
dredge-up in R Hya. V441 Cyg, on the other hand, could either be a low-mass,
intrinsic S-star that produced its large amount of Li by extra-mixing
processes, or an intermediate-mass star (M>=M_sun) undergoing Li production due
to hot bottom burning.Comment: 12 pages, 7 figures, accepted for publication in A&
The Sun was not born in M 67
Using the most recent proper-motion determination of the old,
Solar-metallicity, Galactic open cluster M 67, in orbital computations in a
non-axisymmetric model of the Milky Way, including a bar and 3D spiral arms, we
explore the possibility that the Sun once belonged to this cluster. We have
performed Monte Carlo numerical simulations to generate the present-day orbital
conditions of the Sun and M 67, and all the parameters in the Galactic model.
We compute 3.5 \times 10^5 pairs of orbits Sun-M 67 looking for close
encounters in the past with a minimum distance approach within the tidal radius
of M 67. In these encounters we find that the relative velocity between the Sun
and M 67 is larger than 20 km/s. If the Sun had been ejected from M 67 with
this high velocity by means of a three-body encounter, this interaction would
destroy an initial circumstellar disk around the Sun, or disperse its already
formed planets. We also find a very low probability, much less than 10^-7, that
the Sun was ejected from M 67 by an encounter of this cluster with a giant
molecular cloud. This study also excludes the possibility that the Sun and M 67
were born in the same molecular cloud. Our dynamical results convincingly
demonstrate that M67 could not have been the birth cluster of our Solar System.Comment: Astronomical Journal accepted (35 pages, 9 figures
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