Molecular gas associated with IRAS 10361-5830

We analyze the distribution of the molecular gas and the dust in the molecular clump linked to IRAS 10361-5830, located in the environs of the bubble-shaped HII region Gum 31 in the Carina region, with the aim of determining the main parameters of the associated material and investigating the evolutionary state of the young stellar objects identified there. Using the APEX telescope, we mapped the molecular emission in the J=3-2 transition of three CO isotopologues, 12CO, 13CO and C18O, over a 1.5' x 1.5' region around the IRAS position. We also observed the high density tracers CS and HCO+ toward the source. The cold dust distribution was analyzed using submillimeter continuum data at 870 \mu\ obtained with the APEX telescope. Complementary IR and radio data at different wavelengths were used to complete the study of the ISM. The molecular gas distribution reveals a cavity and a shell-like structure of ~ 0.32 pc in radius centered at the position of the IRAS source, with some young stellar objects (YSOs) projected onto the cavity. The total molecular mass in the shell and the mean H$_2$ volume density are ~ 40 solar masses and ~(1-2) x 10$^3$ cm$^{-3}$, respectively. The cold dust counterpart of the molecular shell has been detected in the far-IR at 870 \mu\ and in Herschel data at 350 \mu. Weak extended emission at 24 \mu\ from warm dust is projected onto the cavity, as well as weak radio continuum emission. A comparison of the distribution of cold and warm dust, and molecular and ionized gas allows us to conclude that a compact HII region has developed in the molecular clump, indicating that this is an area of recent massive star formation. Probable exciting sources capable of creating the compact HII region are investigated. The 2MASS source 10380461-5846233 (MSX G286.3773-00.2563) seems to be responsible for the formation of the HII region.Comment: Accepted in A&A. 11 pages, 10 Postscript figure

Influencia de la calidad del heno suplementario y la localización de la pastura sobre el rendimiento de bovinos de carne a pastoreo sobre avena

Heifers grazing oat pasture (OP) at two locations in Argentina, Argerich (ARG) and Pasman (PAS), were subjected to one of three different dietary supplement treatments: (1) control (CON, no supplement), (2) sorghum hay (SH), or (3) alfalfa-grass hay (AGH), all provided ad libitum in individual pens. The variables measured were: dry matter (DM) yield and composition of OP, hay intake, average daily weight gain (ADG), rumen pH and NH3-N, and blood mineral levels. DM availability did not limit OP intake. OP crude protein (CP) content ranged from 11.3 to 13% at ARG, and 10.7 to 13.3% at PAS. OP-minerals varied with location; the mean K/(Ca + Mg) ratios were 5.68 meq (ARG) and 4.82 meq (PAS). Heifers ate more AGH (785 g) than SH (684 g; P = 0.08). Hay consumption was 2.88 times greater at PAS than at ARG (P < 0.05). ADG was larger with SH (558 g) and AGH 594 g than with CON treatment (454 g); the average for ARG animals was 571 g compared to 500 g for PAS animals (P <0.05). Rumen pH was lower at 14:30 h (pH 6.7) than at 10:00 h (pH 7.5; P < 0.05). NH3-N values were higher at 14:30 h (19.59 mg dl-1) than at 10:00 h (4.69 mg dl-1; P < 0.05). Plasma Ca (15.50 mg dl–1) and Mg (2.84 mg dl–1) levels were higher in PAS cattle (P < 0.05). Animal performance improved with hay supplementation, but location affected response intensity.Se realizaron tres tratamientos con novillas pastoreando verdeos de avena (VA) en dos localidades de Argentina, Argerich (ARG) y Pasman (PAS): (1) Control (CON, sin suplemento), (2) heno de sorgo (HS), y (3) heno de alfalfa y gramíneas (HAG), suplementados ad libitum en corrales individuales. Evaluamos rendimiento de materia seca (MS) y composición en VA; y en los animales consumo del heno, ganancia diaria de peso (GDP), pH y N-NH3 en rumen, y minerales en sangre. La disponibilidad de MS no limitó el consumo de VA; su proteína bruta (PB) osciló entre 11,3 y 13% (ARG), 10,7 y 13.3% (PAS). Los minerales en VA variaron entre localidades, la relación K/(Ca + Mg) promedió 5,68 meq (ARG) y 4,82 meq (PAS). Las novillas consumieron diariamente más HAG (785 g) que HS (684 g; P = 0.08), y 2,88 veces más heno en PAS que en ARG (P < 0,05). En GDP, HS (558 g) y HAG (594 g) superaron al CON (454 g), y la media de ARG (571 g) a PAS (500 g; P < 0,05). En el rumen el pH decreció a las 14:30 h (6,7) vs. 10:00 h (7,5; P < 0,05), y el N-NH3 (mg dl-1) aumentó a las 14:30 h (19,59) vs. 10:00 h (4,69; P < 0,05). Ca (15.50 mg dl–1) y Mg (2.84 mg dl–1) en plasma fue mayor en PAS (P < 0,05). El rendimiento animal mejoró con la suplementación, pero la magnitud de respuesta estuvo afectada por la localidad.Fil: Arelovich, Hugo Mario. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; ArgentinaFil: Laborde, Hugo Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; ArgentinaFil: Arzadún, M. J.. Provincia de Buenos Aires. Ministerio de la Producción. Chacra Experimental Coronel Suarez; ArgentinaFil: Vasquez, Maria Gabriela. Universidad Nacional del Sur. Departamento de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentin

Convective Fingering of an Autocatalytic Reaction Front

We report experimental observations of the convection-driven fingering instability of an iodate-arsenous acid chemical reaction front. The front propagated upward in a vertical slab; the thickness of the slab was varied to control the degree of instability. We observed the onset and subsequent nonlinear evolution of the fingers, which were made visible by a {\it p}H indicator. We measured the spacing of the fingers during their initial stages and compared this to the wavelength of the fastest growing linear mode predicted by the stability analysis of Huang {\it et. al.} [{\it Phys. Rev. E}, {\bf 48}, 4378 (1993), and unpublished]. We find agreement with the thickness dependence predicted by the theory.Comment: 11 pages, RevTex with 3 eps figures. To be published in Phys Rev E, [email protected], [email protected], [email protected]

Molecular gas and star formation towards the IR dust bubble S24 and its environs

We present a multi-wavelength analysis of the infrared dust bubble S24, and its environs, with the aim of investigating the characteristics of the molecular gas and the interstellar dust linked to them, and analyzing the evolutionary status of the young stellar objects (YSOs) identified there. Using APEX data, we mapped the molecular emission in the CO(2-1), $^{13}$CO(2-1), C$^{18}$O(2-1), and $^{13}$CO(3-2) lines in a region of about 5'x 5' in size around the bubble. The cold dust distribution was analyzed using ATLASGAL and Herschel images. Complementary IR and radio data were also used.The molecular gas linked to the S24 bubble, G341.220-0.213, and G341.217-0.237 has velocities between -48.0 km sec$^{-1}$ and -40.0 km sec$^{-1}$. The gas distribution reveals a shell-like molecular structure of $\sim$0.8 pc in radius bordering the bubble. A cold dust counterpart of the shell is detected in the LABOCA and Herschel images.The presence of extended emission at 24 $\mu$m and radio continuum emission inside the bubble indicates that the bubble is a compact HII region. Part of the molecular gas bordering S24 coincides with the extended infrared dust cloud SDC341.194-0.221. A cold molecular clump is present at the interface between S24 and G341.217-0.237. As regards G341.220-0.213, the presence of an arc-like molecular structure at the northern and eastern sections of this IR source indicates that G341.220-0.213 is interacting with the molecular gas. Several YSO candidates are found to be linked to the IR extended sources, thus confirming their nature as active star-forming regions. The total gas mass in the region and the H$_2$ ambient density amount to 10300 M$_{\odot}$ and 5900 cm$^{-3}$, indicating that G341.220-0.213, G341.217-0.237, and the S24 HII region are evolving in a high density medium. A triggering star formation scenario is also investigated.Comment: 17 pages, 16 figures. Submitted to A&A. Revised according to the referee repor

870 micron continuum observations of the bubble-shaped nebula Gum 31

We are presenting here a study of the cold dust in the infrared ring nebula Gum 31. We aim at deriving the physical properties of the molecular gas and dust associated with the nebula, and investigating its correlation with the star formation in the region, that was probably triggered by the expansion of the ionization front. We use 870 micron data obtained with LABOCA to map the dust emission. The obtained LABOCA image was compared to archival IR,radio continuum, and optical images. The 870 micron emission follows the 8 micron (Spitzer), 250 micron, and 500 micron (Herschel) emission distributions showing the classical morphology of a spherical shell. We use the 870 micron and 250 micron images to identify 60 dust clumps in the collected layers of molecular gas using the Gaussclumps algorithm. The clumps have effective deconvolved radii between 0.16 pc and 1.35 pc, masses between 70 Mo and 2800 Mo, and volume densities between 1.1x10^3 cm^-3 and 2.04x10^5 cm^-3. The total mass of the clumps is 37600 Mo. The dust temperature of the clumps is in the range from 21 K to 32 K, while inside the HII region reaches ~ 40 K. The clump mass distribution is well-fitted by a power law dN/dlog(M/Mo) proportional to M^(-alpha), with alpha=0.93+/-0.28. The slope differs from those obtained for the stellar IMF in the solar neighborhood, suggesting that the clumps are not direct progenitors of single stars/protostars. The mass-radius relationship for the 41 clumps detected in the 870 microns emission shows that only 37% of them lie in or above the high-mass star formation threshold, most of them having candidate YSOs projected inside. A comparison of the dynamical age of the HII region with the fragmentation time, allowed us to conclude that the collect and collapse mechanism may be important for the star formation at the edge of Gum 31, although other processes may also be acting.Comment: 15 pages, 10 figures. Accepted for publication in A&

Helical structures from an isotropic homopolymer model

We present Monte Carlo simulation results for square-well homopolymers at a series of bond lengths. Although the model contains only isotropic pairwise interactions, under appropriate conditions this system shows spontaneous chiral symmetry breaking, where the chain exists in either a left- or a right-handed helical structure. We investigate how this behavior depends upon the ratio between bond length and monomer radius.Comment: 10 pages, 3 figures, accepted for publication by Physical Review Letter

Effective gravity from a quantum gauge theory in Euclidean space-time

We consider a $SO(d)$ gauge theory in an Euclidean $d$-dimensional space-time, which is known to be renormalizable to all orders in perturbation theory for $2\le{d}\le4$. Then, with the help of a space-time representation of the gauge group, the gauge theory is mapped into a curved space-time with linear connection. Further, in that mapping the gauge field plays the role of the linear connection of the curved space-time and an effective metric tensor arises naturally from the mapping. The obtained action, being quadratic in the Riemann-Christoffel tensor, at a first sight, spoils a gravity interpretation of the model. Thus, we provide a sketch of a mechanism that breaks the $SO(d)$ color invariance and generates the Einstein-Hilbert term, as well as a cosmological constant term, allowing an interpretation of the model as a modified gravity in the Palatini formalism. In that sense, gravity can be visualized as an effective classical theory, originated from a well defined quantum gauge theory. We also show that, in the four dimensional case, two possibilities for particular solutions of the field equations are the de Sitter and Anti de Sitter space-times.Comment: 20 pages; Final version accepted for publication in Class.Quant.Gra