40,972 research outputs found
Complex hyperbolic free groups with many parabolic elements
We consider in this work representations of the of the fundamental group of
the 3-punctured sphere in such that the boundary loops are
mapped to . We provide a system of coordinates on the
corresponding representation variety, and analyse more specifically those
representations corresponding to subgroups of -groups. In
particular we prove that it is possible to construct representations of the
free group of rank two \la a,b\ra in for which , ,
, , , and all are mapped to parabolics.Comment: 21 pages, 11 figure
Filtered derivative with p-value method for multiple change-points detection
This paper deals with off-line detection of change points for time series of
independent observations, when the number of change points is unknown. We
propose a sequential analysis like method with linear time and memory
complexity. Our method is based at first step, on Filtered Derivative method
which detects the right change points but also false ones. We improve Filtered
Derivative method by adding a second step in which we compute the p-values
associated to each potential change points. Then we eliminate as false alarms
the points which have p-value smaller than a given critical level. Next, our
method is compared with the Penalized Least Square Criterion procedure on
simulated data sets. Eventually, we apply Filtered Derivative with p-Value
method to segmentation of heartbeat time series
About the Efficiency of Input vs. Output Quotas
Output quotas are known to be more efficient than input quotas in transferring surplus from consumers to producers. Input quotas, by distorting the shadow prices of inputs, lead to inefficient production and generate larger deadweight losses, for a given amount of surplus transferred. Yet, input quotas have been a ubiquitous tool in agricultural policy. Practicality considerations, as well as the difficulty to control outputs that heavily depend on stochastic weather conditions, are arguments that help understand why policy makers may favor input quotas over output quotas. In this paper, we offer an additional explanation that rests on efficiency considerations. Assuming that the regulator only has limited knowledge about the market fundamentals (supply and demand elasticities, among others), seeks to transfer at least a given amount of surplus to producers and is influenced by the industry in his choice of the quota level, we show that an input quota becomes the optimal policy.Agricultural and Food Policy, H2, L2, Q1,
Is There Market Power in the French Comte Cheese Market?
An NEIO approach is used to measure seller market power in the French Comté cheese market, characterised by government-approved supply control. The estimation is performed on quarterly data at the wholesale stage over the period 1985-2005. Three different elasticity shifters are included in the demand specification, and the supply equation accounts for the existence of the European dairy quota policy. The market power estimate is small and statistically insignificant. Monopoly is rejected, as well as weak forms of Cournot oligopoly. Results appear to be robust to the choice of functional form, and suggest little effect of the supply control scheme on consumer prices.Supply control, NEIO, protected designation of origin, Marketing,
The dwarf nova SS Cygni: what is wrong?
Since the Fine Guiding Sensor (FGS) on the Hubble Space Telescope (HST) was
used to measure the distance to SS Cyg to be pc, it became apparent
that at this distance the disc instability model fails to explain the absolute
magnitude during outburst. It remained, however, an open question whether the
model or the distance have to be revised. Recent observations led to a revision
of the system parameters of SS Cyg and seem to be consistent with a distance of
d\gta 140 pc. We re-discuss the problem taking into account the new binary
and stellar parameters measured for SS Cyg. We confront not only the
observations with the predictions of the disc instability model but also
compare SS Cyg with other dwarf novae and nova-like systems. We assume the disc
during outburst to be in a quasi stationary state and use the black-body
approximation to estimate the accretion rate during outburst as a function of
distance. Using published analysis of the long term light curve we determine
the mean mass transfer rate of SS Cyg as a function of distance and compare the
result with mass transfer rates derived for other dwarf novae and nova-like
systems. At a distance of d\gta 140 pc, both the accretion rate during
outburst as well as the mean mass transfer rate of SS Cyg contradict the disc
instability model. More important, at such distances we find the mean mass
transfer rate of SS Cyg to be higher or comparable to those derived for
nova-like systems. Our findings show that a distance to SS Cyg \gta 140 pc
contradicts the main concepts developed for accretion discs in cataclysmic
variables during the last 30 years. Either our current picture of disc
accretion in these systems must be revised or the distance to SS Cyg is pcComment: 6 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
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