2,756 research outputs found
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
Mutual information in random Boolean models of regulatory networks
The amount of mutual information contained in time series of two elements
gives a measure of how well their activities are coordinated. In a large,
complex network of interacting elements, such as a genetic regulatory network
within a cell, the average of the mutual information over all pairs is a
global measure of how well the system can coordinate its internal dynamics. We
study this average pairwise mutual information in random Boolean networks
(RBNs) as a function of the distribution of Boolean rules implemented at each
element, assuming that the links in the network are randomly placed. Efficient
numerical methods for calculating show that as the number of network nodes
N approaches infinity, the quantity N exhibits a discontinuity at parameter
values corresponding to critical RBNs. For finite systems it peaks near the
critical value, but slightly in the disordered regime for typical parameter
variations. The source of high values of N is the indirect correlations
between pairs of elements from different long chains with a common starting
point. The contribution from pairs that are directly linked approaches zero for
critical networks and peaks deep in the disordered regime.Comment: 11 pages, 6 figures; Minor revisions for clarity and figure format,
one reference adde
Determination of Arsenic, Mercury and Barium in herbarium mount paper using dynamic ultrasound-assisted extraction prior to atomic fluorescence and absorption spectrometry
A dynamic ultrasound-assisted extraction method using Atomic Absorption and Atomic Flourescence spectrometers as detectors was developed to analyse mercury, arsenic and barium from herbarium mount paper originating from the herbarium collection of the National Museum of Wales. The variables influencing extraction were optimised by a multivariate approach. The optimal conditions were found to be 1% HNO3 extractant solution used at a flow rate of 1 mL min-1. The duty cycle and amplitude of the ultrasonic probe was found to be 50% in both cases with an ultrasound power of 400 W. The optimal distance between the probe and the top face of the extraction chamber was found to be 0 cm. Under these conditions the time required for complete extraction of the three analytes was 25 min. Cold vapour and hydride generation coupled to atomic fluorescence spectrometry was utilized to determine mercury and arsenic, respectively. The chemical and instrumental conditions were optimized to provide detection limits of 0.01ng g-1 and 1.25 ng g-1 for mercury and arsenic, respectively. Barium was determined by graphite-furnace atomic absorption spectrometry, with a detection limit of 25 ng g-1. By using 0.5 g of sample, the concentrations of the target analytes varied for the different types of paper and ranged between 0.4–2.55 µg g-1 for Ba, 0.035–10.47 µg g-1 for As and 0.0046–2.37 µg g-1 for Hg
Chaos control in random Boolean networks by reducing mean damage percolation rate
Chaos control in Random Boolean networks is implemented by freezing part of
the network to drive it from chaotic to ordered phase. However, controlled
nodes are only viewed as passive blocks to prevent perturbation spread. This
paper proposes a new control method in which controlled nodes can exert an
active impact on the network. Controlled nodes and frozen values are
deliberately selected according to the information of connection and Boolean
functions. Simulation results show that the number of nodes needed to achieve
control is largely reduced compared to previous method. Theoretical analysis is
also given to estimate the least fraction of nodes needed to achieve control.Comment: 10 pages, 2 figure
Towards accurate solvation free energies of large biological systems
Continuum solvation models like PCM or COSMO are the standard tool to calculate solvation free energies in a quantum level, but have been typically limited to small biological molecules due to its large computational cost. Recently, a new implementation of COSMO based on a domain decomposition strategy (ddCOSMO) [1] has been presented, which speeds up calculations by several orders of magnitude, thus paving the way for its application to very large systems. Here, we report the parameterization of ddCOSMO to the prediction of hydration free energies based on the MST solvation model developed in Barcelona, [2][3]. The parameterization is based on the PM6 semi-empirical Hamiltonian, on a set of over 200 experimental hydration free energies. The new model opens the way to the accurate prediction of hydration free energies of very large biomolecules, thus going beyond the usual classical MM-PBSA or MM-GBSA approaches
Non-traumatic chronic shoulder pain is not associated with changes in rotator cuff interval tendon thickness
To determine whether the thickness of the rotator interval tendons is different when comparing both symptomatic and non-symptomatic sides in people with chronic shoulder pain, and to those free of pain. Furthermore, to calculate the level of association between the rotator interval tendon thicknesses and perceived shoulder pain-function. A cross-sectional, observational study. The supraspinatus, subscapularis and biceps brachii tendon thickness of sixty two patients with chronic shoulder pain were determined from standardized ultrasonography measures performed on both shoulders, whereas only the dominant arm was measured for the control subjects. Supraspinatus, subscapularis and biceps brachii tendon thickness was comparable between sides in the symptomatic group and was also comparable between the symptomatic and asymptomatic participants. In addition, the correlation between the tendon thickness and shoulder pain-function was non-significant. Tendon thickness was unaltered in people with chronic shoulder pain. These findings do not rule out the possibility that other changes in the tendon are present such as changes in the elastic properties and cell population and this should be explored in future studies
3-D properties of pulsed corona streamers
Properties of pulsed corona streamers are measured and simulated in full three spatial dimensions (3D). Stereo photography is used to measure branching angles and to investigate whether apparent streamers reconnections are real. 3D simulations of two parallel streamers show that they can repel each other electrostatically, but that they also can merge due to photoionization. The electrostatic interaction of several streamers becomes evident through theoretical investigations of a periodic array of streamers
Classification of qubit entanglement: SL(2,C) versus SU(2) invariance
The role of SU(2) invariants for the classification of multiparty
entanglement is discussed and exemplified for the Kempe invariant I_5 of pure
three-qubit states. It is found to being an independent invariant only in
presence of both W-type entanglement and threetangle. In this case, constant
I_5 admits for a wide range of both threetangle and concurrences. Furthermore,
the present analysis indicates that an SL^3 orbit of states with equal tangles
but continuously varying I_5 must exist. This means that I_5 provides no
information on the entanglement in the system in addition to that contained in
the tangles (concurrences and threetangle) themselves. Together with the
numerical evidence that I_5 is an entanglement monotone this implies that SU(2)
invariance or the monotone property are too weak requirements for the
characterization and quantification of entanglement for systems of three
qubits, and that SL(2,C) invariance is required. This conclusion can be
extended to general multipartite systems (including higher local dimension)
because the entanglement classes of three-qubit systems appear as subclasses.Comment: 9 pages, 10 figures, revtex
Extending the scope of microscopic solvability: Combination of the Kruskal-Segur method with Zauderer decomposition
Successful applications of the Kruskal-Segur approach to interfacial pattern
formation have remained limited due to the necessity of an integral formulation
of the problem. This excludes nonlinear bulk equations, rendering convection
intractable. Combining the method with Zauderer's asymptotic decomposition
scheme, we are able to strongly extend its scope of applicability and solve
selection problems based on free boundary formulations in terms of partial
differential equations alone. To demonstrate the technique, we give the first
analytic solution of the problem of velocity selection for dendritic growth in
a forced potential flow.Comment: Submitted to Europhys. Letters, No figures, 5 page
Valoración naturalística del Corredor Verde del Río Guadiamar Andalucía, España)
En este trabajo aplicamos un método de valoración naturalística, concretamente el índice de interés para la conservación, a cada una de las unidades de un mapa de vegetación previamente realizado a escala 1:10.000. Para el cálculo de los distintos criterios de valoración se tienen en cuenta las comunidades vegetales (asociaciones) presentes en cada unidad, en vez de las especies como suele ser habitual. Las unidades del mapa están agrupadas en series de vegetación, por lo que también pueden extraerse conclusiones sobre el grado de conservación de cada una de ellas. Los resultados se plasman en un mapa de interés para la conservación. El escenario en el que se realizó el trabajo es el corredor verde del río Guadiamar, situado en el sur de España. La zona fue afectada por un vertido tóxico y lo que aquí mostramos son los resultados obtenidos tras una primera limpieza. Después se han iniciado trabajos de restauración, al cabo de los cuales podremos realizar un estudio comparativo con los resultados de este trabajo.In this paper we have applied a naturalistic evaluation strategy, more precisely, the conservation importance index, to each unit of a preplanned 1:10.000scale vegetation map. The estimation of the different evaluation criteria is based on the plant communities (associations) found in each unit rather than on species, as is usual. Since the map units are grouped in vegetation series, the conservation degree of each of them can also be assessed. The results are presented in a conservation interest map. The survey was undertaken in the Green Corridor of the Guadiamar River, in the south of Spain. The area was affected by a toxic spill and our data refl ect the results obtained after the fi rst stage of cleaning work. Subsequently, restoration work has been undertaken after which we will be able to carry out a comparative analysis with the results of this work.Junta de Andalucía. Consejería de Medio Ambiente
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