59,746 research outputs found
Systems And Methods For Detection Of Combustor Stability Margin
The present invention comprises systems and methods for determining stability margin of a combustor. One embodiment of the present invention includes the steps of providing a measuring device in communication with the combustor, wherein the measuring device generates signals indicative of combustor quantities; performing an autocorrelation calculation on the signals to determine the correlation time of the signals in the combustor; and determining the damping coefficient from the autocorrelation calculation, wherein the damping coefficient signifies a proximity of the combustor to instability. The damping coefficient may be estimated from the oscillatory envelope of the autocorrelation calculation data.Georgia Tech Research Corporatio
Kinetochore alignment within the metaphase plate is regulated by centromere stiffness and microtubule depolymerases
During mitosis in most eukaryotic cells, chromosomes align and form a metaphase plate halfway between the spindle poles, about which they exhibit oscillatory movement. These movements are accompanied by changes in the distance between sister kinetochores, commonly referred to as breathing. We developed a live cell imaging assay combined with computational image analysis to quantify the properties and dynamics of sister kinetochores in three dimensions. We show that baseline oscillation and breathing speeds in late prometaphase and metaphase are set by microtubule depolymerases, whereas oscillation and breathing periods depend on the stiffness of the mechanical linkage between sisters. Metaphase plates become thinner as cells progress toward anaphase as a result of reduced oscillation speed at a relatively constant oscillation period. The progressive slowdown of oscillation speed and its coupling to plate thickness depend nonlinearly on the stiffness of the mechanical linkage between sisters. We propose that metaphase plate formation and thinning require tight control of the state of the mechanical linkage between sisters mediated by centromeric chromatin and cohesion
Spatial Models to Account for Variation in Observer Effort in Bird Atlases
To assess the importance of variation in observer effort between and within bird atlas projects and demonstrate the use of relatively simple conditional autoregressive (CAR) models for analyzing grid-based atlas data with varying effort. Pennsylvania and West Virginia, United States of America. We used varying proportions of randomly selected training data to assess whether variations in observer effort can be accounted for using CAR models and whether such models would still be useful for atlases with incomplete data. We then evaluated whether the application of these models influenced our assessment of distribution change between two atlas projects separated by twenty years (Pennsylvania), and tested our modeling methodology on a state bird atlas with incomplete coverage (West Virginia). Conditional Autoregressive models which included observer effort and landscape covariates were able to make robust predictions of species distributions in cases of sparse data coverage. Further, we found that CAR models without landscape covariates performed favorably. These models also account for variation in observer effort between atlas projects and can have a profound effect on the overall assessment of distribution change. Accounting for variation in observer effort in atlas projects is critically important. CAR models provide a useful modeling framework for accounting for variation in observer effort in bird atlas data because they are relatively simple to apply, and quick to run
Early warning signals: The charted and uncharted territories
The realization that complex systems such as ecological communities can
collapse or shift regimes suddenly and without rapid external forcing poses a
serious challenge to our understanding and management of the natural world. The
potential to identify early warning signals that would allow researchers and
managers to predict such events before they happen has therefore been an
invaluable discovery that offers a way forward in spite of such seemingly
unpredictable behavior. Research into early warning signals has demonstrated
that it is possible to define and detect such early warning signals in advance
of a transition in certain contexts. Here we describe the pattern emerging as
research continues to explore just how far we can generalize these results. A
core of examples emerges that shares three properties: the phenomenon of rapid
regime shifts, a pattern of 'critical slowing down' that can be used to detect
the approaching shift, and a mechanism of bifurcation driving the sudden
change. As research has expanded beyond these core examples, it is becoming
clear that not all systems that show regime shifts exhibit critical slowing
down, or vice versa. Even when systems exhibit critical slowing down,
statistical detection is a challenge. We review the literature that explores
these edge cases and highlight the need for (a) new early warning behaviors
that can be used in cases where rapid shifts do not exhibit critical slowing
down, (b) the development of methods to identify which behavior might be an
appropriate signal when encountering a novel system; bearing in mind that a
positive indication for some systems is a negative indication in others, and
(c) statistical methods that can distinguish between signatures of early
warning behaviors and noise
A multivariate model for financial indices and an algorithm for detection of jumps in the volatility
We consider a mean-reverting stochastic volatility model which satisfies some
relevant stylized facts of financial markets. We introduce an algorithm for the
detection of peaks in the volatility profile, that we apply to the time series
of Dow Jones Industrial Average and Financial Times Stock Exchange 100 in the
period 1984-2013. Based on empirical results, we propose a bivariate version of
the model, for which we find an explicit expression for the decay over time of
cross-asset correlations between absolute returns. We compare our theoretical
predictions with empirical estimates on the same financial time series, finding
an excellent agreement.Comment: 20 pages, 22 figure
Atom detection in a two-mode optical cavity with intermediate coupling: Autocorrelation studies
We use an optical cavity in the regime of intermediate coupling between atom
and cavity mode to detect single moving atoms. Degenerate polarization modes
allow excitation of the atoms in one mode and collection of spontaneous
emission in the other, while keeping separate the two sources of light; we
obtain a higher confidence and efficiency of detection by adding
cavity-enhanced Faraday rotation. Both methods greatly benefit from coincidence
detection of photons, attaining fidelities in excess of 99% in less than 1
microsecond. Detailed studies of the second-order intensity autocorrelation
function of light from the signal mode reveal evidence of antibunched photon
emissions and the dynamics of single-atom transits.Comment: 10 pages, 10 figures, to be published in Phys. Rev.
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