1,361 research outputs found
The Rotating Molecular Structures and the Ionized Outflow Associated with IRAS 16547-4247
We present VLA 1.3 cm radio continuum and water maser observations as well as
SMA SO (226.300 GHz) and 1.3 mm dust continuum observations toward the
massive star formation region IRAS 16547-4247. We find evidence of multiple
sources in the central part of the region. There is evidence of a rotating
structure associated with the most massive of these sources, traced at small
scales (~50 AU) by the water masers. At large scales (~1000 AU) we find a
velocity gradient in the SO2 molecular emission with a barely resolved
structure that can be modeled as a rotating ring or two separate objects. The
velocity gradients of the masers and of the molecular emission have the same
sense and may trace the same structure at different size scales. The position
angles of the structures associated with the velocity gradients are roughly
perpendicular to the outflow axis observed in radio continuum and several
molecular tracers. We estimate the mass of the most massive central source to
be around 30 solar masses from the velocity gradient in the water maser
emission. The main source of error in this estimate is the radius of the
rotating structure. We also find water masers that are associated with the
large scale molecular outflow of the system, as well as water masers that are
associated with other sources in the region. Our results suggest that the
formation of this source, one of the most luminous protostars or protostellar
clusters known, is taking place with the presence of ionized jets and disk-like
structures.Comment: 26 pages, 7 figure
Tropical Grass Growth Functions Modeling by Using Nonlinear Mixed Models
Nonlinear Growth curves are used for modeling plant physiological variables. These models are preferable because the polynomial coefficients of the equations have a biological significance. The response variables of the curves occurs commonly with repeated measurements over time and measurements are on different environments. The traditional statistical analysis does not include a repeated measures approach, which can lead to improper estimation of the error terms. It is important to study the growth of tropical grass (Da Silva and Carvalho 2005)
A wide-angle outflow with the simultaneous presence of a high-velocity jet in the high-mass Cepheus A HW2 system
We present five epochs of VLBI water maser observations around the massive
protostar Cepheus A HW2 with 0.4 mas (0.3 AU) resolution. The main goal of
these observations was to follow the evolution of the remarkable water maser
linear/arcuate structures found in earlier VLBI observations. Comparing the
data of our new epochs of observation with those observed five years before, we
find that at "large" scales of > 1" (700 AU) the main regions of maser emission
persist, implying that both the surrounding medium and the exciting sources of
the masers have been relatively stable during that time span. However, at
smaller scales of < 0.1" (70 AU) we see large changes in the maser structures,
particularly in the expanding arcuate structures R4 and R5. R4 traces a nearly
elliptical patchy ring of ~ 70 mas size (50 AU) with expanding motions of ~ 5
mas/yr (15 km/s). This structure is probably driven by the wind of a still
unidentified YSO located at the centre of the ring (~ 0.18" south of HW2). On
the other hand, the R5 expanding bubble structure (driven by the wind of a
previously identified YSO located ~ 0.6" south of HW2) is currently dissipating
in the circumstellar medium and losing its previous degree of symmetry,
indicating a very short-lived event. In addition, our results reveal, at scales
of ~ 1" (700 AU), the simultaneous presence of a relatively slow (~ 10-70 km/s)
wide-angle outflow (opening angle of ~ 102 deg, traced by the masers, and the
fast (~ 500~km/s) highly collimated radio jet associated with HW2 (opening
angle of ~ 18 deg, previously observed with the VLA. This simultaneous presence
of a wide-angle outflow and a highly collimated jet associated with a massive
protostar is similar to what is found in some low-mass YSOs. The implications
of these results in the study of the formation of high-mass stars are
discussed.Comment: 28 pages, 7 figures. Animations will be included as supporting
material online (MNRAS web page
Methanol maps of low-mass protostellar systems: the Serpens Molecular Core
Observations of Serpens have been performed at the JCMT using Harp-B. Maps
over a 4.5'x5.4' region were made in a frequency window around 338 GHz,
covering the 7-6 transitions of methanol. Emission is extended over each
source, following the column density of H2 but showing up also particularly
strongly around outflows. The rotational temperature is low, 15-20 K, and does
not vary with position within each source. The abundance is typically 10^-9 -
10^-8 with respect to H2 in the outer envelope, whereas "jumps" by factors of
up to 10^2 -10^3 inside the region where the dust temperature exceeds 100 K are
not excluded. A factor of up to ~ 10^3 enhancement is seen in outflow gas. In
one object, SMM4, the ice abundance has been measured to be ~ 3x10^-5 with
respect to H2 in the outer envelope, i.e., a factor of 10^3 larger than the
gas-phase abundance. Comparison with C18O J=3-2 emission shows that strong CO
depletion leads to a high gas-phase abundance of CH3OH not just for the Serpens
sources, but for a larger sample of protostars. The observations illustrate the
large-scale, low-level desorption of CH3OH from dust grains, extending out to
and beyond 7500 AU from each source, a scenario which is consistent with
non-thermal (photo-)desorption from the ice. The observations also illustrate
the usefulness of CH3OH as a tracer of energetic input in the form of outflows,
where methanol is sputtered from the grain surfaces. Finally, the observations
provide further evidence of CH3OH formation through CO hydrogenation proceeding
on grain surfaces in low-mass envelopes.Comment: Accepted for publication in A&A
Análisis de crecimiento del pasto Toledo Urochloa brizantha (Hochst. ex A. Rich.) R.D. Webster en clima cálido subhúmedo
Objective: Perform a growth analysis of Toledo grass (Urochloa brizantha CIAT 26110) during de rainy season, from sowing to 180 days, to determine the optimum harvesting moment. Design/methodology/approach: The morphological composition (CM), growth rate (GR), plant height, intercepted radiation (RI), leaf / stem ratio (L:S), leaf / non-leaf (L:NL), and biomass accumulation were evaluated every fifteen days during a 180 days period, except for the first two samples (monthly). Data were analyzed using the GLM procedure of SAS, under an experimental design of randomized blocks, with repeated measures over time, with three replicates. Results: The CM varied significantly (P<0.01) through the different physiological states. The maximum production of aerial biomass (19.9 t DM ha-1) and GR (131.9 kg DM ha-1 day-1) were reached 150 days after sowing (dap) and that of leaves (3.9 t DM ha-1) was at 135 dap. At this time the RI was 100% and the height of plant was 106 cm. Limitations on study/implications: Toledo grass should be planted in the rainy season to be used when the canopy reaches a coverage greater than 80%, because the proportion of leaves decreases as the age of the plant progresses. Findings/conclusions: The highest accumulated total biomass, so it is suggested that the cut be made at 135 days after plantingObjetivo: realizar un análisis de crecimiento del pasto Toledo (Urochloa brizantha CIAT 26110) en la época de lluvias, desde la siembra hasta los 180 días, para determinar el momento óptimo de cosecha. Diseño/metodología/aproximación: Se evaluó la composición morfológica (CM), tasa de crecimiento (TC), altura de planta, radiación interceptada (RI), relación hoja/tallo (H:T), hoja/no hoja (H:NH) y la acumulación de biomasa aérea, a intervalos de quince días, a excepción de los dos primeros muestreos que fueron mensuales. Los datos fueron analizados mediante el procedimiento GLM de SAS, bajo un diseño experimental de bloques al azar, con medidas repetidas en el tiempo, con tres repeticiones. Resultados: La CM varió (P£0.01) a través de los diferentes estados fisiológicos. La máxima producción de biomasa aérea (19.9 t MS ha-1) y TC (131.9 kg MS ha-1 día-1) se alcanzó a los 150 días después de la siembra (dds), y la de hojas (3.9 t MS ha-1) fue a los 135 dds, en este momento la RI fue del 100% y la altura de 106 cm. Limitaciones del estudio/implicaciones: El pasto Toledo debe ser sembrado a inicio de la época de lluvias para ser usado cuando la cobertura del suelo sea mayor a 80 %, debido a que la proporción de hojas decrece conforme avanza la edad de la planta. Hallazgos/conclusiones: La máxima TC coincidió con la mayor biomasa total acumulada a los 135 (dds), por lo que se sugiere realizar el corte en este momento
Geoelectrical and electromagnetic methods applied to paleolimnological studies: Two examples from desiccated lakes in the Basin of Mexico
Paleolimnological studies require a broad understanding of the geometry and depth of the sedimentary fill of lake basins prior to coring campaigns. Seismic methods are routinely employed for the indirect characterization of lake-bottom sediments. However, the use of seismic methods might occasionally be limited due to surface conditions or poor seismic contrasts between the stratigraphic units, which lead to data quality that is too poor to provide sufficient information for the selection of drill sites. Sources of cultural noise are one of the main reasons why seismic methods fail in study areas near or within large cities, such as Mexico City. Under certain conditions, electrical and electromagnetic methods might be a suitable substitute or complement to seismic exploration, as they respond to different physical properties of the subsurface. To evaluate the applicability of such methods, here we present two recent case studies from the desiccated lakes Chalco and Xochimilco both located in urban areas within the Basin of Mexico where electrical resistivity tomography (ERT), transient electromagnetic (TEM) and magnetotelluric (MT) soundings were conducted for the characterization of lake basement and lacustrine sediments. In both examples, the results of the geophysical exploration contributed valuable stratigraphic information for the following drilling and core recovery, which highlights the potential of electrical and electromagnetic methods in paleolimnological studies
The CHESS chemical Herschel surveys of star forming regions: Peering into the protostellar shock L1157-B1. I. Shock chemical complexity
We present the first results of the unbiased survey of the L1157-B1 bow
shock, obtained with HIFI in the framework of the key program Chemical Herschel
surveys of star forming regions (CHESS). The L1157 outflow is driven by a
low-mass Class 0 protostar and is considered the prototype of the so-called
chemically active outflows. The bright blue-shifted bow shock B1 is the ideal
laboratory for studying the link between the hot (around 1000-2000 K) component
traced by H2 IR-emission and the cold (around 10-20 K) swept-up material. The
main aim is to trace the warm gas chemically enriched by the passage of a shock
and to infer the excitation conditions in L1157-B1. A total of 27 lines are
identified in the 555-636 GHz region, down to an average 3 sigma level of 30
mK. The emission is dominated by CO(5-4) and H2O(110-101) transitions, as
discussed by Lefloch et al. (2010). Here we report on the identification of
lines from NH3, H2CO, CH3OH, CS, HCN, and HCO+. The comparison between the
profiles produced by molecules released from dust mantles (NH3, H2CO, CH3OH)
and that of H2O is consistent with a scenario in which water is also formed in
the gas-phase in high-temperature regions where sputtering or grain-grain
collisions are not efficient. The high excitation range of the observed tracers
allows us to infer, for the first time for these species, the existence of a
warm (> 200 K) gas component coexisting in the B1 bow structure with the cold
and hot gas detected from ground
Dominant Negative Mutants of Bacillus thuringiensis Cry1Ab Toxin Function as Anti-Toxins: Demonstration of the Role of Oligomerization in Toxicity
BACKGROUND:Bacillus thuringiensis Cry toxins, that are used worldwide in insect control, kill insects by a mechanism that depends on their ability to form oligomeric pores that insert into the insect-midgut cells. These toxins are being used worldwide in transgenic plants or spray to control insect pests in agriculture. However, a major concern has been the possible effects of these insecticidal proteins on non-target organisms mainly in ecosystems adjacent to agricultural fields. METHODOLOGY/PRINCIPAL FINDINGS:We isolated and characterized 11 non-toxic mutants of Cry1Ab toxin affected in different steps of the mechanism of action namely binding to receptors, oligomerization and pore-formation. These mutant toxins were analyzed for their capacity to block wild type toxin activity, presenting a dominant negative phenotype. The dominant negative phenotype was analyzed at two levels, in vivo by toxicity bioassays against susceptible Manduca sexta larvae and in vitro by pore formation activity in black lipid bilayers. We demonstrate that some mutations located in helix alpha-4 completely block the wild type toxin activity at sub-stoichiometric level confirming a dominant negative phenotype, thereby functioning as potent antitoxins. CONCLUSIONS/SIGNIFICANCE:This is the first reported case of a Cry toxin dominant inhibitor. These data demonstrate that oligomerization is a fundamental step in Cry toxin action and represent a potential mechanism to protect special ecosystems from the possible effect of Cry toxins on non-target organisms
Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at s√=8 TeV with the ATLAS detector
The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. The search is based on proton-proton collision data at a centre-of-mass energy s√=8 TeV collected in 2012, corresponding to an integrated luminosity of 20 fb−1. No significant excess above the Standard Model expectation is observed. Limits are set on supersymmetric particle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV. Limits are also set on the parameters of a minimal universal extra dimension model, excluding a compactification radius of 1/R c = 950 GeV for a cut-off scale times radius (ΛR c) of approximately 30
Evidence for the Higgs-boson Yukawa coupling to tau leptons with the ATLAS detector
Results of a search for H → τ τ decays are presented, based on the full set of proton-proton collision data recorded by the ATLAS experiment at the LHC during 2011 and 2012. The data correspond to integrated luminosities of 4.5 fb−1 and 20.3 fb−1 at centre-of-mass energies of √s = 7 TeV and √s = 8 TeV respectively. All combinations of leptonic (τ → `νν¯ with ` = e, µ) and hadronic (τ → hadrons ν) tau decays are considered. An excess of events over the expected background from other Standard Model processes is found with an observed (expected) significance of 4.5 (3.4) standard deviations. This excess provides evidence for the direct coupling of the recently discovered Higgs boson to fermions. The measured signal strength, normalised to the Standard Model expectation, of µ = 1.43 +0.43 −0.37 is consistent with the predicted Yukawa coupling strength in the Standard Model
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