3,924 research outputs found
Spatial distribution of X-ray emitting ejecta in Tycho's SNR: indications of shocked Titanium
Young supernova remnants show a characteristic ejecta-dominated X-ray
emission that allows us to probe the products of the explosive nucleosynthesis
processes and to ascertain important information about the physics of the
supernova explosions. Hard X-ray observations have recently revealed the
radioactive decay lines of 44Ti at ~67.9 keV and ~78.4 keV in the Tycho's SNR.
We here analyze the set of XMM-Newton archive observations of the Tycho's SNR.
We produce equivalent width maps of the Fe K and Ca XIX emission lines and find
indications for a stratification of the abundances of these elements and
significant anisotropies. We then perform a spatially resolved spectral
analysis by identifying five different regions characterized by high/low values
of the Fe K equivalent width. We find that the spatial distribution of the Fe K
emission is correlated with that of the Cr XXII. We also detect the Ti K-line
complex in the spectra extracted from the two regions with the highest values
of the Fe and Cr equivalent widths. The Ti line emissions remains undetected in
regions where the Fe and Cr equivalent widths are low. Our results indicate
that the post-shock Ti is spatially co-located with other iron-peak nuclei in
Tycho's SNR, in agreement with the predictions of multi-D models of Type Ia
supernovae.Comment: Accepted for publication in Ap
La ciencia de las redes
Obra ressenyada: D. J. WATTS, Six Degrees : the Science of a Connected Ag
Direct numerical simulations of mass transfer in square microchannels for liquid-liquid slug flow
Microreactors for the development of liquid-liquid processes are promising technologies since they are supposed to offer an enhancement of mass transfer compared to conventional devices due to the increase of the surface/volume ratio. But impact of the laminar flow should be negative and the effect is still to be evaluated. The present work focuses on the study of mass transfer in microchannels by means of 2D direct numerical simulations. We investigated liquid-liquid slug flow systems in square channel of 50 to 960 ÎĽm depth. The droplets velocity ranges from 0.0015 to 0.25 m/s and the ratio between the channel depth and the droplets length varies between 0.4 and 11.2. Droplet side volumetric mass transfer coefficients were identified from concentration field computations and the evolution of these coefficients as a function of the flow parameters and the channel size is discussed. This study reveals that mass transfer is strongly influenced by the flow structure inside the droplet. Moreover, it shows that the confinement of the droplets due to the channel size leads to an enhancement of mass transfer compared to cases where the droplets are not constrained by the walls
Modeling non-thermal emission from stellar bow shocks
Runaway O- and early B-type stars passing throughout the interstellar medium
at supersonic velocities and characterized by strong stellar winds may produce
bow shocks that can serve as particle acceleration sites. Previous theoretical
models predict the production of high energy photons by non-thermal radiative
processes, but their efficiency is still debated. We aim to test and explain
the possibility of emission from the bow shocks formed by runaway stars
traveling through the interstellar medium by using previous theoretical models.
We apply our model to AE Aurigae, the first reported star with an X-ray
detected bow shock, to BD+43 3654, in which the observations failed in
detecting high energy emission, and to the transition phase of a supergiant
star in the late stages of its life.From our analysis, we confirm that the
X-ray emission from the bow shock produced by AE Aurigae can be explained by
inverse Compton processes involving the infrared photons of the heated dust. We
also predict low high energy flux emission from the bow shock produced by BD+43
3654, and the possibility of high energy emission from the bow shock formed by
a supergiant star during the transition phase from blue to red supergiant.Bow
shock formed by different type of runaway stars are revealed as a new possible
source of high energy photons in our neighbourhood
Optimisation of operating conditions in batch for more sustainable continuous process transposition
Implementation of exothermic and fast reactions requires a perfect temperature control to avoid thermal runaway and in most cases to limit by-products production. In order to fit with the heat removal capacity of common devices, expensive strategies are currently used to slow down this kind of reactions in order to avoid a strong temperature increase such as reactants dilution. Within the concept of process intensification, industries could move towards more sustainable process by reducing technology constraints to the benefit of chemistry. For that purpose, a two-step methodology is implemented. The first step consists in the optimisation of the operating conditions only based on stoichio-chemical scheme and kinetic laws. This is carried out by adjusting temperature profile and feeding rate strategy in a batch operation. Then a design for a continuous process is proposed, trying to approach the optimal batch operating conditions. This methodology is applied to the linear alkylbenzene sulfonation
Mixing characterization inside microdroplets engineered on a microcoalescer
We use a microdevice where microdroplets of reagents are generated and coalesce in a carrier continuous phase. The work focuses on the characterization of the mixing step inside the droplets, in the perspective to use them for chemical kinetic data acquisition. A dye and water are used, and an acid–base instantaneous chemical reaction is monitored thanks to a colored indicator. Acquisitions are done with a high-speed camera coupled to a microscope and a mixing parameter is calculated by image analysis. Different angles of bended channels and different ways of coalescence are compared. It is shown that the homogenization of the droplets can be reached in less than 10 ms after coalescence.
This is achieved by forcing the droplets to coalesce in a “shifted” way, and later by adding 45◦ angle bends along the channel
Software de GenealogĂas
Teniendo como antecedente la elaboraciĂłn de un trabajo analĂtico centrado en el vĂnculo parentesco-posesiĂłn de ganado en la reserva patagĂłnica tehuelche del ChalĂa, en el sur argentino, tuvimos como meta la automatizaciĂłn de las complejas tareas de carga de informaciĂłn que antes habĂamos ejecutado manualmente. El resultado de esta preocupaciĂłn es el programa que presentamos, que consta básicamente de un mĂłdulo de carga de datos parentales, capaz de mapear en diagramas arbolados las relaciones de descendencia que ligan a los miembros de una comunidad, y un mĂłdulo de generaciĂłn de una matriz relacional procesable directamente por programas de ARS como el UCINET y PAJEK. Las diferentes representaciones generadas pueden almacenarse tanto en archivos de Excel como en archivos de texto con formato nativo directamente compatible con los programas nombrados, lo cual permite una extrapolaciĂłn directa y sin intervenciĂłn humana de la informaciĂłn ingresada por la interfase de carga. El desarrollo de esta aplicaciĂłn nos otorga varias ventajas por sobre los mĂ©todos manuales de volcado de informaciĂłn. El proceso es mucho más veloz, consistente y confiable que apelando al ingreso manual, y además se pueden recorrer y modificar los datos de manera completamente intuitiva y clara, sin luchar con las dificultades inherentes a la interacciĂłn directa con la base de datos en su formato relacional. Además, la alimentaciĂłn de informaciĂłn realizada por esta vĂa se desarrolla echando mano a la misma semántica del problema que se quiere analizar, cosa imposible de hacer si el usuario ejecuta la carga en la interfase del software final especializado en manejo de ARS
An X-ray characterization of the central region of the SNR G332.5-5.6
We present an X-ray analysis of the central region of supernova remnant (SNR)
G332.5-5.6 through an exhaustive analysis of XMM-Netwon observations with
complementary infrared observations. We characterize and discuss the origin of
the observed X-ray morphology, which presents a peculiar plane edge over the
west side of the central region. The morphology and spectral properties of the
X-ray supernova remnant were studied using a single full frame XMM-Newton
observation in the 0.3 to 10.0 keV energy band. Archival infrared WISE
observations at 8, 12 and 24 \mu m were also used to investigate the properties
of the source and its surroundings at different wavelengths. The results show
that the extended X-ray emission is predominantly soft (0.3-1.2 keV) and peaks
around 0.5 keV, which shows that it is an extremely soft SNR. X-ray emission
correlates very well with central regions of bright radio emission. On the west
side the radio/X-ray emission displays a plane-like feature with a terminal
wall where strong infrared emission is detected. Our spatially resolved X-ray
spectral analysis confirms that the emission is dominated by weak atomic
emission lines of N, O, Ne, and Fe, all of them undetected in previous X-ray
studies. These characteristics suggest that the X-ray emission is originated in
an optically thin thermal plasma, whose radiation is well fitted by a
non-equilibrium ionization collisional plasma (VNEI) X-ray emission model. Our
study favors a scenario where G332.5-5.6 is expanding in a medium with an
abrupt density change (the wall), likely a dense infrared emitting region of
dust on the western side of the source.Comment: 7 pages, 5 figures and 2 tables. Accepted for publication in A&
Detailed study of SNR G306.3-0.9 using XMM-Newton and Chandra observations
We used combined data from XMM-Newton and Chandra observatories to study the
X-ray morphology of SNR G306.3-0.9. A spatially-resolved spectral analysis was
used to obtain physical and geometrical parameters of different regions of the
remnant. Spitzer infrared observations were also used to constrain the
progenitor supernova and study the environment in which the SNR evolved. The
X-ray morphology of the remnant displays a non-uniform structure of
semi-circular appearance, with a bright southwest region and very weak or
almost negligible X-ray emission in its northern part. These results indicate
that the remnant is propagating in a non-uniform environment as the shock
fronts are encountering a high-density medium, where enhanced infrared emission
is detected. The X-ray spectral analysis of the selected regions shows distinct
emission-line features of several metal elements, confirming the thermal origin
of the emission. The X-ray spectra are well represented by a combination of two
absorbed thermal plasma models: one in equilibrium ionization with a mean
temperature of ~0.19 keV, and another out of equilibrium ionization at a higher
temperature of ~1.1 or 1.6-1.9 keV. For regions located in the northeast,
central, and southwest part of the SNR, we found elevated abundances of Si, S,
Ar, Ca, and Fe, typical of ejecta material. The outer regions located northwest
and south show values of the abundances above solar but lower than to those
found in the central regions. This suggests that the composition of the
emitting outer parts of the SNR is a combination of ejecta and shocked material
of the interstellar medium. The comparison between the S/Si, Ar/Si, and Ca/Si
abundances ratios (1.75, 1.27, and 2.72 in the central region, respectively),
favor a Type Ia progenitor for this SNR, a result that is also supported by an
independent morphological analysis using X-ray and IR data.Comment: 8 pages, 7 figures. Accepted by Astronomy and Astrophysic
Seismic reliability analysis of isolated deck bridges using friction pendulum devices
In this study, the seismic reliability of multi-span continuous deck bridges equipped with isolation friction pendulum (FP) devices is investigated. The relevant aleatory uncertainties associated to the sliding friction coefficient of the FP isolators and to the seismic inputs are considered. A six-degree-of-freedom model is established to reproduce the elastic behavior of the reinforced concrete (RC) pier, the stiff response of the deck supported by the isolation devices and the non-linear response of the FPS bearings which depends on the sliding velocity. Moreover, the RC abutment is assumed as infinitely rigid. For what concerns the seismic inputs, a group of natural seismic records having various characteristics is adopted and properly scaled to increasing levels of intensity. The random variability of the friction coefficient is modelled by suitable probabilistic distribution. Then, considering several bridges and isolator configurations, the fragility curves of the RC pier and of the isolator devices (FP) are determined. Finally, in agreement with the hazard curve of the specific site, the convolution integral is adopted to determine the seismic reliability curves in the performance domain
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