558 research outputs found
Strong practical stability based robust stabilization of uncertain discrete linear repetitive processes
Repetitive processes are a distinct class of 2D systems of both theoretical and practical interest whose dynamics evolve over a subset of the positive quadrant in the 2D plane. The stability theory for these processes originally consisted of two distinct concepts termed asymptotic stability and stability along the pass respectively where the former is a necessary condition for the latter. Stability along the pass demands a bounded-input bounded-output property over the complete positive quadrant of the 2D plane and this is a very strong requirement, especially in terms of control law design. A more feasible alternative for some cases is strong practical stability, where previous work has formulated this property and obtained necessary and sufficient conditions for its existence together with Linear Matrix Inequality (LMI) based tests, which then extend to allow control law design. This paper develops considerably simpler, and hence computationally more efficient, stability tests that extend to allow control law design in the presence of uncertainty in process model
Floral structure of Kirkia (Kirkiaceae) and its position in Sapindales
BACKGROUND AND AIMS: The monogeneric Kirkiaceae (Sapindales) were formerly placed as Kirkioideae in Simaroubaceae. However, recent molecular phylogenetic studies indicate that they are not in Simaroubaceae and they appear to be sister to the clade of Anacardiaceae plus Burseraceae. Such affinity was never considered or discussed since the first description of Kirkia. The present study is the first detailed analysis of the floral structure of a representative of Kirkiaceae and the first comparison with other sapindalean families, especially Anacardiaceae and Burseraceae. METHODS: Floral structure of Kirkia wilmsii was studied using transversal and longitudinal microtome section series, scanning electron microscopy and light microscopy. KEY RESULTS: The flowers of Kirkia wilmsii are morphologically bisexual but functionally unisexual. They are polysymmetric, isomerous (tetramerous) and haplostemonous. The ovary is syncarpous and entirely synascidiate. The floral apex forms a hemispherical protrusion on top of the ovary. The styles are free but postgenitally united and apically form a stigmatic head with a compitum. Each carpel is uniovulate (biovulate in a few other species) and ovules are crassinucellar, bitegmic and slightly campylotropous. The micropyle is formed by both integuments and is unusually long. The unusual two radially disposed locules in each carpel in the former genus Pleiokirkia can be explained developmentally by the two offset and tightly contiguous lateral placentae. CONCLUSIONS: Paralleling the molecular results, a suite of floral features supports the position of Kirkiaceae close to the Anacardiaceae-Burseraceae clade, and not in Simaroubacea
Caractéristiques pédologiques et microbiologiques des sols de la station RCP 40 de la forêt de Sénart et du parc de Brunoy
An Outlook on Correlations in Stock Prices
We present an outlook of the studies on correlations in the price timeseries
of stocks, discussing the construction and applications of "asset tree". The
topic discussed here should illustrate how the complex economic system
(financial market) enrichens the list of existing dynamical systems that
physicists have been studying for long.Comment: 6 pages, RevTeX format. To appear in the Conference Proceedings of
ECONOPHYS-KOLKATA II: International Workshop on Econophysics of Stock Markets
and Minority Games", February 14-17, 2006, SINP, Kolkata, as a book chapter
in Eds. A. Chatterjee and B.K. Chakrabarti, Econophysics of Stock and other
Markets, (Springer-Verlag (Italia), Milan, 2006
Collective behavior of stock price movements in an emerging market
To investigate the universality of the structure of interactions in different
markets, we analyze the cross-correlation matrix C of stock price fluctuations
in the National Stock Exchange (NSE) of India. We find that this emerging
market exhibits strong correlations in the movement of stock prices compared to
developed markets, such as the New York Stock Exchange (NYSE). This is shown to
be due to the dominant influence of a common market mode on the stock prices.
By comparison, interactions between related stocks, e.g., those belonging to
the same business sector, are much weaker. This lack of distinct sector
identity in emerging markets is explicitly shown by reconstructing the network
of mutually interacting stocks. Spectral analysis of C for NSE reveals that,
the few largest eigenvalues deviate from the bulk of the spectrum predicted by
random matrix theory, but they are far fewer in number compared to, e.g., NYSE.
We show this to be due to the relative weakness of intra-sector interactions
between stocks, compared to the market mode, by modeling stock price dynamics
with a two-factor model. Our results suggest that the emergence of an internal
structure comprising multiple groups of strongly coupled components is a
signature of market development.Comment: 10 pages, 10 figure
Analysis of aggregated tick returns: evidence for anomalous diffusion
In order to investigate the origin of large price fluctuations, we analyze
stock price changes of ten frequently traded NASDAQ stocks in the year 2002.
Though the influence of the trading frequency on the aggregate return in a
certain time interval is important, it cannot alone explain the heavy tailed
distribution of stock price changes. For this reason, we analyze intervals with
a fixed number of trades in order to eliminate the influence of the trading
frequency and investigate the relevance of other factors for the aggregate
return. We show that in tick time the price follows a discrete diffusion
process with a variable step width while the difference between the number of
steps in positive and negative direction in an interval is Gaussian
distributed. The step width is given by the return due to a single trade and is
long-term correlated in tick time. Hence, its mean value can well characterize
an interval of many trades and turns out to be an important determinant for
large aggregate returns. We also present a statistical model reproducing the
cumulative distribution of aggregate returns. For an accurate agreement with
the empirical distribution, we also take into account asymmetries of the step
widths in different directions together with crosscorrelations between these
asymmetries and the mean step width as well as the signs of the steps.Comment: 9 pages, 10 figures, typos correcte
Vortex-forced-oscillations of thin flexible plates
Fluid-structure interaction of a slender flexible cantilevered-element and
vortices in an otherwise steady flow is considered here by investigating the
dynamics of thin low-density polyethylene sheets subject to periodic forcing
due to B\'enard-K\`arm\`an vortices in a -meter long narrow water channel.
The vortex shedding frequency is varied via the mean flow speed and
the cylinder diameter , and mm, while the structures'
bending resistance is properly controlled via its Young's modulus ,
thickness and length . Thereby, it is first shown that the
non-dimensional time-averaged sheet deflection, namely, the sheet
\textit{reconfiguration} and also, the
time-averaged \textit{drag force} ,
where is the well-known Vogel number for flexible
structures in a steady flow and is the Cauchy number
comparing the relative magnitude of the profile drag force over a typical
elastic restoring force, if the sheet were rigid. Measurements and a simple
model based on torsional-spring-mounted flat plate illustrate that the tip
amplitude is not only directly proportional to the characteristic
size of the eddies, say , but also to the sheet mechanical properties and
the vortex flow characteristics such that . Furthermore, a rich phenomenology
of structural dynamics including vortex-forced-vibration, lock-in with the
sheet natural frequency, flow-induced vibration due to the sheet wake,
multiple-frequency and modal response is reported
Determinants of immediate price impacts at the trade level in an emerging order-driven market
The common wisdom argues that, in general, large trades cause large price
changes, while small trades cause small price changes. However, for extremely
large price changes, the trade size and news play a minor role, while the
liquidity (especially price gaps on the limit order book) is a more influencing
factor. Hence, there might be other influencing factors of immediate price
impacts of trades. In this paper, through mechanical analysis of price
variations before and after a trade of arbitrary size, we identify that the
trade size, the bid-ask spread, the price gaps and the outstanding volumes at
the bid and ask sides of the limit order book have impacts on the changes of
prices. We propose two regression models to investigate the influences of these
microscopic factors on the price impact of buyer-initiated partially filled
trades, seller-initiated partially filled trades, buyer-initiated filled
trades, and seller-initiated filled trades. We find that they have
quantitatively similar explanation powers and these factors can account for up
to 44% of the price impacts. Large trade sizes, wide bid-ask spreads, high
liquidity at the same side and low liquidity at the opposite side will cause a
large price impact. We also find that the liquidity at the opposite side has a
more influencing impact than the liquidity at the same side. Our results shed
new lights on the determinants of immediate price impacts.Comment: 21 IOP tex pages including 5 figures and 5 tables. Accepted for
publication in New Journal of Physic
- …