2,541 research outputs found
Spectroscopic diagnostics of dust formation and evolution in classical nova ejecta
A fraction of classical novae form dust during the early stages of their
outbursts. The classical CO nova V5668 Sgr (Nova Sgr. 2015b) underwent a deep
photometric minimum about 100 days after outburst that was covered across the
spectrum. A similar event was observed for an earlier CO nova, V705 Cas (Nova
Cas 1993) and a less optically significant event for the more recent CO nova
V339 Del (Nova Del 2013). This study provides a "compare and contrast" of these
events to better understand the very dynamical event of dust formation. We show
the effect of dust formation on multiwavelength high resolution line profiles
in the interval 1200\AA\ - 9200\AA\ using a biconical ballistic structure that
has been applied in our previous studies of the ejecta. We find that both V5668
Sgr and V339 Del can be modeled using a grey opacity for the dust, indicating
fairly large grains (at least 0.1 micron) and that the persistent asymmetries
of the line profiles in late time spectra, up to 650 days after the event for
V5668 Sgr and 866 days for V339 Del, point to the survival of the dust well
into the transparent, nebular stage of the ejecta evolution. This is a general
method for assessing the properties of dust forming novae well after the
infrared is completely transparent in the ejecta.Comment: 15 pages 14 figures, accepted for publication in A&A, 2018 June 2
Introduction: emotions and mobilities: gendered, temporal and spatial representations
Emotions are increasingly recognised as a fundamental dimension of human mobility. Indeed, there has been sustained and increasing scholarly interest in the intersection between migration and emotion over the last two decades.Theoretical and empirical contributions in this area have advanced our understanding of migration experiences in their diversity. Furthermore, viewing migrantsâ lived experiences through an emotions lens can reveal a variety of hidden inequalities, unsettle hegemonic discourses and reveal practices of resistance.Perceptions of social categories such as ethnicity, gender, sexuality and age are shaped by emotions and it is therefore valuable to âinvestigate how certain emotions âstickâ to certain bodies or flow and traverse spaceâ
Nurses Practice Beyond Simple Advocacy to Engage in Relational Narratives: Expanding Opportunities for Persons to Influence the Public Space
In practicing existential and human advocacy, or engaging in a relational narrative, nurses may assist persons who experience health inequalities to clarify their values, and, in becoming more fully their authentic selves, community members who ordinarily feel powerless in the public space may act with confidence in influencing the distribution of health-care resources. In this paper, the writers describe research characterizing nursesâ advocacy practices and review the concepts of respect and self-interpretation as a foundation for arguing that nurses who engage in relational narratives with the persons they serve may encourage continuing acts of self-understanding. Investigators indicated that nurses characterized their practices as a therapeutic endeavor, and that their practices were grounded in respect. Practicing nurses may need self-awareness to habitually convey respect for human dignity, in addition, nurse educators ought to attend to the professional development of student nurses, providing opportunities for the formation of character traits or qualities
Brownian motion of a charged particle driven internally by correlated noise
We give an exact solution to the generalized Langevin equation of motion of a
charged Brownian particle in a uniform magnetic field that is driven internally
by an exponentially-correlated stochastic force. A strong dissipation regime is
described in which the ensemble-averaged fluctuations of the velocity exhibit
transient oscillations that arise from memory effects. Also, we calculate
generalized diffusion coefficients describing the transport of these particles
and briefly discuss how they are affected by the magnetic field strength and
correlation time. Our asymptotic results are extended to the general case of
internal driving by correlated Gaussian stochastic forces with finite
autocorrelation times.Comment: 10 pages, 4 figures with subfigures, RevTeX, v2: revise
Optimal receptor-cluster size determined by intrinsic and extrinsic noise
Biological cells sense external chemical stimuli in their environment using
cell-surface receptors. To increase the sensitivity of sensing, receptors often
cluster, most noticeably in bacterial chemotaxis, a paradigm for signaling and
sensing in general. While amplification of weak stimuli is useful in absence of
noise, its usefulness is less clear in presence of extrinsic input noise and
intrinsic signaling noise. Here, exemplified on bacterial chemotaxis, we
combine the allosteric Monod-Wyman- Changeux model for signal amplification by
receptor complexes with calculations of noise to study their
interconnectedness. Importantly, we calculate the signal-to-noise ratio,
describing the balance of beneficial and detrimental effects of clustering for
the cell. Interestingly, we find that there is no advantage for the cell to
build receptor complexes for noisy input stimuli in absence of intrinsic
signaling noise. However, with intrinsic noise, an optimal complex size arises
in line with estimates of the sizes of chemoreceptor complexes in bacteria and
protein aggregates in lipid rafts of eukaryotic cells.Comment: 15 pages, 12 figures,accepted for publication on Physical Review
The spectroscopic evolution of the recurrent nova T Pyxidis during its 2011 outburst. II.The optically thin phase and the structure of the ejecta in recurrent novae
We continue our study of the physical properties of the recurrent nova T Pyx,
focussing on the structure of the ejecta in the nebular stage of expansion
during the 2011 outburst. The nova was observed contemporaneously with the
Nordic Optical Telescope (NOT), at high resolution spectroscopic resolution (R
~ 65000) on 2011 Oct. 11 and 2012 Apr. 8 (without absolute flux calibration),
and with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble
Space Telescope, at high resolution (R ~ 30000) on 2011 Oct. 10 and 2012 Mar.
28 (absolute fluxes). We use standard plasma diagnostics (e.g. [O III] and [N
II] line ratios and the H line fluxes) to constrain electron densities
and temperatures. Using Monte Carlo modeling of the ejecta, we derive the
structure and filling factor from comparisons to the optical and ultraviolet
line profiles. The ejecta can be modeled using an axisymmetric conical --
bipolar -- geometry with a low inclination of the axis to the line of sight,
i=15+/-5 degrees, compatible with published results from high angular
resolution optical spectro-interferometry. The structure is similar to that
observed in the other short orbital period recurrent novae during their nebular
stages. We show that the electron density scales as as expected from a
ballistically ejected constant mass shell; there is no need to invoke a
continuing mass outflow following the eruption. The derived mass for the ejecta
with filling factor f ~ 3%, M_ej ~ 2E-6$M_sun is similar to that obtained for
other recurrent nova ejecta but inconsistent with the previously reported
extended optically thick epoch of the explosion. We suggest that the system
underwent a common envelope phase following the explosion that produced the
recombination event. Implications for the dynamics of the recurrent novae are
discussed. (truncated)Comment: accepted for publication in A&A (10 Nov. 2012), 10 pgs, 16 fig
The spectroscopic evolution of the -ray emitting classical nova Nova Mon 2012. I. Implications for the ONe subclass of classical novae
Nova Mon 2012 was the first classical nova to be detected as a high energy
-ray transient, by Fermi-LAT, before its optical discovery. We study a
time sequence of high resolution optical echelle spectra (Nordic Optical
Telescope) and contemporaneous NOT, STIS UV, and CHIRON echelle spectra (Nov
20/21/22). We use [O III] and H line fluxs to constrain the properties
of the ejecta. We derive the structure from the optical and UV line profiles
and compare our measured line fluxes for with predictions using Cloudy with
abundances from other ONe novae. Mon 2012 is confirmed as an ONe nova. We find
E(B-V)=0.850.05 and hydrogen column density
cm. The corrected continuum luminosity is nearly the same in the entire
observed energy range as V1974 Cyg, V382 Mon, and Nova LMC 2000 at the same
epoch after outburst. The distance, about 3.6 kpc, is quite similar to V1974
Cyg. The line profiles can be modeled using an axisymmetric bipolar geometry
for the ejecta with various inclinations of the axis to the line of sight, 60
\le i \le 80 degrees, an opening angle of \approx\Delta
R/R(t)\approx 0.4f\approx 0.1-0.3\leq 6\times
10^{-5}_\odot\gamma$-ray emission may be a generic phenomenon, common to all ONe novae,
possibly to all classical novae, and connected with acceleration and emission
processes within the ejecta (abstract severely truncated).Comment: Submitted to A&A 9/1/2013; Accepted 27/2/2013 (in press
Correlation in the velocity of a Brownian particle induced by frictional anisotropy and magnetic field
We study the motion of charged Brownian particles in an external magnetic
field. It is found that a correlation appears between the components of
particle velocity in the case of anisotropic friction, approaching
asymptotically zero in the stationary limit. If magnetic field is smaller
compared to the critical value, determined by frictional anisotropy, the
relaxation of the correlation is non-oscillating in time. However, in a larger
magnetic field this relaxation becomes oscillating. The phenomenon is related
to the statistical dependence of the components of transformed random force
caused by the simultaneous influence of magnetic field and anisotropic
dissipation.Comment: 7 pages, 2 figure
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