748 research outputs found
Fundamental stellar and accretion disc parameters of the eclipsing binary DQ Velorum
To add to the growing collection of well-studied double periodic variables
(DPVs) we have carried out the first spectroscopic and photometric analysis of
the eclipsing binary DQ Velorum to obtain its main physical stellar and orbital
parameters. Combining spectroscopic and photometric observations that cover
several orbital cycles allows us to estimate the stellar properties of the
binary components and the orbital parameters. We also searched for
circumstellar material around the more massive star. We separated DQ Velorum
composite spectra and measured radial velocities with an iterative method for
double spectroscopic binaries. We obtained the radial velocity curves and
calculated the spectroscopic mass ratio. We compared our single-lined spectra
with a grid of synthetic spectra and estimated the temperature of the stars. We
modeled the V-band light curve with a fitting method based on the simplex
algorithm, which includes an accretion disc. To constrain the main stellar
parameters we fixed the mass ratio and donor temperature to the values obtained
by our spectroscopic analysis. We obtain donor and gainer masses, the radii,
and temperatures for the stellar components. We find that DQ Vel is a
semi-detached system consisting of a B3V gainer and an A1III donor star plus an
extended accretion disc around the gainer. The disc is filling 89% of the
gainer Roche lobe and it has a concave shape that is thicker at its edge than
at its centre. We find a significant sub-orbital frequency of 0.19 d^{-1} in
the residuals of the V-band light curve, which we interpret as a pulsation of
an slowly pulsating B-type (SPB) of a gainer star. We also estimate the
distance to the binary (3.1 kpc) using the absolute radii, apparent magnitudes,
and effective temperatures of the components found in our study.Comment: 12 pages, 13 Postscript figure
Optical spectroscopy of DPVs and the case of LP Ara
We present preliminary results of our spectroscopic campaign of a group of
intermediate mass interacting binaries dubbed "Double Periodic Variables"
(DPVs), characterized by orbital light curves and additional long photometric
cycles recurring roughly after 33 orbital periods (Mennickent et al. 2003,
2005). They have been interpreted as interacting, semi-detached binaries
showing cycles of mass loss into the interstellar medium (Mennickent et al.
2008, Mennickent & Kolaczkowski 2009). High resolution Balmer and helium line
profiles of DPVs can be interpreted in terms of mass flows in these systems. A
system solution is given for LP Ara, based on modeling of the ASAS V-band
orbital light curve and the radial velocity of the donor star.Comment: To be published in the proceedings book of the IAUS 272, Cambridge
University Press. Editors C. Neiner, G. Wade, G. Meynet and G. Peter
Adaptive Horizon Model Predictive Control and Al'brekht's Method
A standard way of finding a feedback law that stabilizes a control system to
an operating point is to recast the problem as an infinite horizon optimal
control problem. If the optimal cost and the optmal feedback can be found on a
large domain around the operating point then a Lyapunov argument can be used to
verify the asymptotic stability of the closed loop dynamics. The problem with
this approach is that is usually very difficult to find the optimal cost and
the optmal feedback on a large domain for nonlinear problems with or without
constraints. Hence the increasing interest in Model Predictive Control (MPC).
In standard MPC a finite horizon optimal control problem is solved in real time
but just at the current state, the first control action is implimented, the
system evolves one time step and the process is repeated. A terminal cost and
terminal feedback found by Al'brekht's methoddefined in a neighborhood of the
operating point is used to shorten the horizon and thereby make the nonlinear
programs easier to solve because they have less decision variables. Adaptive
Horizon Model Predictive Control (AHMPC) is a scheme for varying the horizon
length of Model Predictive Control (MPC) as needed. Its goal is to achieve
stabilization with horizons as small as possible so that MPC methods can be
used on faster and/or more complicated dynamic processes.Comment: arXiv admin note: text overlap with arXiv:1602.0861
Implications of GATT for Eastern Europe and the Baltics
The story of agriculture in Eastern Europe during the last quarter century is a story of policy driven by politics, rather than by sound economics. Even in the highly distorted economics of the socialist period, agricultural policy stands out as being singularly colored by ideological imperatives, and singularly vulnerable to interest group pressures. While the revolutions of 1989-91 did mark a sharp move towards liberalization, these moves are now being slowed and even reversed, as countries of the region adopt Western style interventionism on preparation for accession to the European Union
Novel triblock co-polymer nanofibre system as an alternative support for embryonic stem cells growth and pluripotency
Conventionally, embryonic stem cells (ESCs) are cultured on gelatin or over a mitotically inactivated monolayer of mouse embryonic fibroblasts (MEFsi). Considering the lack of versatile, non-animal-derived and inexpensive materials for that purpose, we aimed to find a biomaterial able to support ESC growth in a pluripotent state that avoids the need for laborious and time-consuming MEFsi culture in parallel with mouse ESC (mESC) culture. Undifferentiated mESCs were cultured in a new nanofibre material designed for ESC culture, which is based on the self-assembly of a triblock co-polymer, poly(ethyleneglycol-β-trimethylsilyl methacrylate-β-methacrylic acid), conjugated with the peptide glycine-arginine-glycine-aspartate-serine, to evaluate its potential application in ESC research. The morphology, proliferation, viability, pluripotency and differentiation potential of mESCs were assessed. Compared to conventional stem cell culture methodologies, the nanofibres promoted a higher increase in mESCs number, enhanced pluripotency and were able to support differentiation after long-term culture. This newly developed synthetic system allows the elimination of animal-derived matrices and provides an economic method of ESC culture, made of a complex network of nanofibres in a scale similar to native extracellular matrices, where the functional properties of the cells can be observed and manipulated
Wirtualizacja i prosumpcja – innowacyjne trendy w konsumpcji turystycznej i ich wpływ na strategie dystrybucji podmiotów organizacji i pośrednictwa w turystyce
The primary purpose of the article is to characterize the two trends in tourism consumption, mutually determining each other, and their impact on the distribution strategies of entities operating in the sector of tourism organization and intermediation. By means of applying the method of scientific publications, both domestic and foreign, review the study explains the concepts of virtualization and prosumption, as well as discusses their manifestations in tourism. The analysis of information collected from many sources, mainly the secondary ones, not only the importance, but also the impact directions of both consumer oriented trends were emphasized on the functioning of tour operators in the area of their offer distribution
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