3,483 research outputs found
Value chain analysis in pro-poor tourism:towards a critical understanding of the contribution of tourism to poverty reduction
Comparison of fringe-tracking algorithms for single-mode near-infrared long-baseline interferometers
To enable optical long baseline interferometry toward faint objects, long
integrations are necessary despite atmospheric turbulence. Fringe trackers are
needed to stabilize the fringes and thus increase the fringe visibility and
phase signal-to-noise ratio (SNR), with efficient controllers robust to
instrumental vibrations, and to subsequent path fluctuations and flux
drop-outs.
We report on simulations, analysis and comparison of the performances of a
classical integrator controller and of a Kalman controller, both optimized to
track fringes under realistic observing conditions for different source
magnitudes, disturbance conditions, and sampling frequencies. The key
parameters of our simulations (instrument photometric performance, detection
noise, turbulence and vibrations statistics) are based on typical observing
conditions at the Very Large Telescope observatory and on the design of the
GRAVITY instrument, a 4-telescope single-mode long baseline interferometer in
the near-infrared, next in line to be installed at VLT Interferometer.
We find that both controller performances follow a two-regime law with the
star magnitude, a constant disturbance limited regime, and a diverging detector
and photon noise limited regime. Moreover, we find that the Kalman controller
is optimal in the high and medium SNR regime due to its predictive commands
based on an accurate disturbance model. In the low SNR regime, the model is not
accurate enough to be more robust than an integrator controller. Identifying
the disturbances from high SNR measurements improves the Kalman performances in
case of strong optical path difference disturbances.Comment: Accepted for publication in A&A. 17 pages 15 figure
What do Bayesian methods offer population forecasters?
The Bayesian approach has a number of attractive properties for probabilistic forecasting. In this paper, we apply Bayesian time series models to obtain future population estimates with uncertainty for England and Wales. To account for heterogeneity found in the historical data, we add parameters to represent the stochastic volatility in the error terms. Uncertainty in model choice is incorporated through Bayesian model averaging techniques. The resulting predictive distributions from Bayesian forecasting models have two main advantages over those obtained using traditional stochastic models. Firstly, data and uncertainties in the parameters and model choice are explicitly included using probability distributions. As a result, more realistic probabilistic population forecasts can be obtained. Second, Bayesian models formally allow the incorporation of expert opinion, including uncertainty, into the forecast. Our results are discussed in relation to classical time series methods and existing cohort component projections. This paper demonstrates the flexibility of the Bayesian approach to simple population forecasting and provides insights into further developments of more complicated population models that include, for example, components of demographic change
Aminoglycoside-Induced Phosphatidylserine Externalization in Sensory Hair Cells Is Regionally Restricted, Rapid, and Reversible
The aminophospholipid phosphatidylserine (PS) is normally restricted to the inner leaflet of the plasma membrane. During certain cellular processes, including apoptosis, PS translocates to the outer leaflet and can be labeled with externally applied annexin V, a calcium-dependent PS-binding protein. In mouse cochlear cultures, annexin V labeling reveals that the aminoglycoside antibiotic neomycin induces rapid PS externalization, specifically on the apical surface of hair cells. PS externalization is observed within ~75 s of neomycin perfusion, first on the hair bundle and then on membrane blebs forming around the apical surface. Whole-cell capacitance also increases significantly within minutes of neomycin application, indicating that blebbing is accompanied by membrane addition to the hair cell surface. PS externalization and membrane blebbing can, nonetheless, occur independently. Pretreating hair cells with calcium chelators, a procedure that blocks mechanotransduction, or overexpressing a phosphatidylinositol 4,5-biphosphate (PIP2)-binding pleckstrin homology domain, can reduce neomycin-induced PS externalization, suggesting that neomycin enters hair cells via transduction channels, clusters PIP2, and thereby activates lipid scrambling. The effects of short-term neomycin treatment are reversible. After neomycin washout, PS is no longer detected on the apical surface, apical membrane blebs disappear, and surface-bound annexin V is internalized, distributing throughout the supranuclear cytoplasm of the hair cell. Hair cells can therefore repair, and recover from, neomycin-induced surface damage. Hair cells lacking myosin VI, a minus-end directed actin-based motor implicated in endocytosis, can also recover from brief neomycin treatment. Internalized annexin V, however, remains below the apical surface, thereby pinpointing a critical role for myosin VI in the transport of endocytosed material away from the periphery of the hair cell
- …