61 research outputs found
Maritime activity in the high north – the range of unwanted incidents and risk patterns
Author's accepted version (post-print).This is the accepted manuscript (post-print) of the article Marchenko, N., Borch, O. J., Markov, S. V. & Andreassen, N. (2015). Maritime activity in the high north – the range of unwanted incidents and risk patterns. Proceedings – International Conference on Port and Ocean Engineering under Arctic Conditions available at http://www.poac.com/PapersOnline.htm
Maritime Safety in The High North - Risk and Preparedness
Author's accepted version (postprint).This is an Accepted Manuscript of an article published by the International Society of Offshore and Polar Engineers in ISOPE - International Society of Offshore and Polar Engineers. Proceedings on 07/2016, available online: http://www.isope.org/publications/proceedings/ISOPE/ISOPE%202016/index.ht
Structure-related bandgap of hybrid lead halide perovskites and close-packed APbX3 family of phases
Metal halide perovskites APbX3 (A+ = FA+ (formamidinium), MA+
(methylammonium) or Cs+, X- = I-, Br-) are considered as prominent innovative
components in nowadays perovskite solar cells. Crystallization of these
materials is often complicated by the formation of various phases with the same
stoichiometry but structural types deviating from perovskites such as
well-known the hexagonal delta FAPbI3 polytype. Such phases are rarely placed
in the focus of device engineering due to their unattractive optoelectronic
properties while they are, indeed, highly important because they influence on
the optoelectronic properties and efficiency of final devices. However, the
total number of such phases has not been yet discovered and the complete
configurational space of the polytypes and their band structures have not been
studied systematically. In this work, we predicted and described all possible
hexagonal polytypes of hybrid lead halides with the APbI3 composition using the
group theory approach, also we analyzed theoretically the relationship between
the configuration of close-packed layers in polytypes and their band gap using
DFT calculations. Two main factors affecting the bandgap were found including
the ratio of cubic (c) and hexagonal (h) close-packed layers and the thickness
of blocks of cubic layers in the structures. We also show that the dependence
of the band gap on the ratio of cubic (c) and hexagonal (h) layers in these
structures are non-linear. We believe that the presence of such polytypes in
the perovskite matrix might be a reason for a decrease in the charge carrier
mobility and therefore it would be an obstacle for efficient charge transport
causing negative consequences for the efficiency of solar cell devices
The puzzle of HD 104994 (WR 46)
Intense coordinated spectroscopic and photometric monitoring of the suspected Wolf-Rayet binary WR 46 in 1999 reveals clear periodic variations, P = 0.329 ± 0.013 days, in the radial velocities of the emission lines of highest ionization potential, O VI and N V, found deepest in the Wolf-Rayet wind and thus least likely to be perturbed by a companion. These are accompanied by coherent variability in the profiles of lines with lower ionization/excitation potential and in the continuum flux. Most probably originating from orbital motion of the Wolf-Rayet component of the binary, this periodic radial velocity signal disappears from time to time, thus creating a puzzle yet to be solved. We show that the entangled patterns of the line profile variability are mainly governed by transitions between high and low states of the system's continuum flux.Facultad de Ciencias Astronómicas y Geofísica
The puzzle of HD 104994 (WR 46)
Intense coordinated spectroscopic and photometric monitoring of the suspected Wolf-Rayet binary WR 46 in 1999 reveals clear periodic variations, P = 0.329 ± 0.013 days, in the radial velocities of the emission lines of highest ionization potential, O VI and N V, found deepest in the Wolf-Rayet wind and thus least likely to be perturbed by a companion. These are accompanied by coherent variability in the profiles of lines with lower ionization/excitation potential and in the continuum flux. Most probably originating from orbital motion of the Wolf-Rayet component of the binary, this periodic radial velocity signal disappears from time to time, thus creating a puzzle yet to be solved. We show that the entangled patterns of the line profile variability are mainly governed by transitions between high and low states of the system's continuum flux.Facultad de Ciencias Astronómicas y Geofísica
A 2.3-Day Periodic Variability in the Apparently Single Wolf-Rayet Star WR 134: Collapsed Companion or Rotational Modulation?
We present the results of an intensive campaign of spectroscopic and
photometric monitoring of the peculiar Wolf-Rayet star WR 134 from 1989 to
1997.
This unprecedentedly large data set allows us to confirm unambiguously the
existence of a coherent 2.25 +/- 0.05 day periodicity in the line-profile
changes of He II 4686, although the global pattern of variability is different
from one epoch to another. This period is only marginally detected in the
photometric data set. Assuming the 2.25 day periodic variability to be induced
by orbital motion of a collapsed companion, we develop a simple model aiming at
investigating (i) the effect of this strongly ionizing, accreting companion on
the Wolf-Rayet wind structure, and (ii) the expected emergent X-ray luminosity.
We argue that the predicted and observed X-ray fluxes can only be matched if
the accretion on the collapsed star is significantly inhibited. Additionally,
we performed simulations of line-profile variations caused by the orbital
revolution of a localized, strongly ionized wind cavity surrounding the X-ray
source. A reasonable fit is achieved between the observed and modeled
phase-dependent line profiles of He II 4686. However, the derived size of the
photoionized zone substantially exceeds our expectations, given the observed
low-level X-ray flux. Alternatively, we explore rotational modulation of a
persistent, largely anisotropic outflow as the origin of the observed cyclical
variability. Although qualitative, this hypothesis leads to greater consistency
with the observations.Comment: 34 pages, 16 figures. Accepted by the Astrophysical Journa
The puzzle of HD 104994 (WR 46)
Intense coordinated spectroscopic and photometric monitoring of the suspected Wolf-Rayet binary WR 46 in 1999 reveals clear periodic variations, P = 0.329 ± 0.013 days, in the radial velocities of the emission lines of highest ionization potential, O VI and N V, found deepest in the Wolf-Rayet wind and thus least likely to be perturbed by a companion. These are accompanied by coherent variability in the profiles of lines with lower ionization/excitation potential and in the continuum flux. Most probably originating from orbital motion of the Wolf-Rayet component of the binary, this periodic radial velocity signal disappears from time to time, thus creating a puzzle yet to be solved. We show that the entangled patterns of the line profile variability are mainly governed by transitions between high and low states of the system's continuum flux.Facultad de Ciencias Astronómicas y Geofísica
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