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

Plasticity of porous NiTi alloys obtained by self-propagating high-temperature synthesis in closed and open gas flow reactors

Porous NiTi alloys were obtained by self-propagating high-temperature synthesis (SHS) using layer-bylayer combustion in closed and open gas flow reactors under a protective argon atmosphere. The maximum compressive strain of porous NiTi alloys synthesized in the closed reactor was 34% compared to 7% in the open gas flow reactor. X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, energy dispersive spectroscopy, and optical microscopy showed that the reaction products in the two-phase gas zone of peritectic crystallization are in the form of isolated Ti2Ni crystalline clusters in the TiNi matrix. The ductility and strength of the recrystallized Ti2Ni phase hard dendrites increase the effective stiffness of porous NiTi alloys and decrease the maximum compressive strain. A highly porous NiTi alloy with improved mechanical properties was obtained by the SHS method in a closed reactor

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