3,418 research outputs found
Quivers and moduli spaces of pointed curves of genus zero
We construct moduli spaces of representations of quivers over arbitrary
schemes and show how moduli spaces of pointed curves of genus zero like the
Grothendieck-Knudsen moduli spaces and the Losev-Manin
moduli spaces can be interpreted as inverse limits of moduli
spaces of representations of certain bipartite quivers. We also investigate the
case of more general Hassett moduli spaces of weighted
pointed stable curves of genus zero.Comment: 41 page
Why Is It So Difficult to Beat the Random Walk Forecast of Exchange Rates?
We propose a stylized exchange rate model based on diversity and weight of opinion. Our model departs from standard assumptions in that we allow for heterogeneous agents. We show that such a model can explain both the observed volatility and the persistence of real and nominal exchange rate movements and thus in some measure resolves Rogoff’s (1996) purchasing power parity puzzle. Our empirical analysis reconciles the well-known difficulties in beating the random walk forecast model with the statistical evidence of nonlinear mean reversion in deviations from fundamentals. We find strong evidence of long-horizon predictability both in theory and in practice. We also explain why it is difficult to exploit this predictability in out-ofsample forecasts. Our results not only lend support to economists’ beliefs that the exchange rate is inherently predictable, but they also help us to understand the reluctance of applied forecasters to abandon chartists methods in favor of models based on economic fundamentals.Purchasing power parity, Real exchange rate, Random walk, Economic models of exchange rate determination, Long-horizon regression tests.
Stochastic maximal -regularity
In this article we prove a maximal -regularity result for stochastic
convolutions, which extends Krylov's basic mixed -inequality for the
Laplace operator on to large classes of elliptic operators,
both on and on bounded domains in with
various boundary conditions. Our method of proof is based on McIntosh's
-functional calculus, -boundedness techniques and sharp
-square function estimates for stochastic integrals in -spaces.
Under an additional invertibility assumption on , a maximal space--time
-regularity result is obtained as well.Comment: Published in at http://dx.doi.org/10.1214/10-AOP626 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
On the R-boundedness of stochastic convolution operators
The -boundedness of certain families of vector-valued stochastic
convolution operators with scalar-valued square integrable kernels is the key
ingredient in the recent proof of stochastic maximal -regularity,
, for certain classes of sectorial operators acting on spaces
, . This paper presents a systematic study of
-boundedness of such families. Our main result generalises the
afore-mentioned -boundedness result to a larger class of Banach lattices
and relates it to the -boundedness of an associated class of
deterministic convolution operators. We also establish an intimate relationship
between the -boundedness of these operators and the boundedness of
the -valued maximal function. This analysis leads, quite surprisingly, to an
example showing that -boundedness of stochastic convolution operators fails
in certain UMD Banach lattices with type .Comment: to appear in Positivit
State Fragility: Concept and Measurement
The international donor community has grave concerns about the prospects for poverty reduction in what it terms fragile states. A state is classified as fragile if its country policy and institutional assessment (CPIA) score falls below a particular threshold. Recognizing that all states are fragile to varying degrees, this paper questions the method used by the international community to deem a country fragile. This paper develops a framework that uses fuzzy-set theory to deem a country as fragile. Fuzzy sets allow for gradual transition from one state to another while also allowing one to incorporate rules and goals, and hence are more appropriate for measuring outcomes that are ambiguous. Such ambiguity is an inherent characteristic of cross-country fragility classifications. The paper applies its framework to 76 low-income countries, for which the CPIA data are publicly available. The fragile state group that this framework provides is compared to that which the international donor community has constructed.fragile states, policies, institutional performance, CPIA scores, fuzzy set theory
Embedding vector-valued Besov spaces into spaces of -radonifying operators
It is shown that a Banach space has type if and only for some (all)
the Besov space embeds into the
space \g(L^2(\R^d),E) of \g-radonifying operators . A
similar result characterizing cotype is obtained. These results may be
viewed as -valued extensions of the classical Sobolev embedding theorems.Comment: To appear in Mathematische Nachrichte
Fuzzy well-being in Pacific Asia
This paper develops a framework that uses fuzzy-set theory to measure human well-being. Fuzzy sets allow for gradual transition from one state to another while also allowing one to incorporate rules and goals, and hence are more appropriate for measuring outcomes that are ambiguous. Such ambiguity is an inherent characteristic of cross-country achieved well-being assessments. This framework is used to provide a fuzzy representation of the well known Human Development Index (HDI) and its three components. Fuzzy HDI estimates for 14 Pacific Asian countries are provided and compared with non-fuzzy estimates. Quite large differences in rankings emerge. The paper concludes by suggesting that fuzzy measures should be used more widely to measure achieved well-being outcomes.<br /
Aliquoting structure for centrifugal microfluidics based on a new pneumatic valve
We present a new microvalve that can be monolithically integrated in centrifugally driven lab-on-a-chip systems. In contrast to existing operation principles that use hydrophobic patches, geometrically defined capillary stops or siphons, here we present a pneumatic principle. It needs neither additional local coatings nor expensive micro sized geometries. The valve is controlled by the spinning frequency and can be switched to be open when the centrifugal pressure overcomes the pneumatic pressure inside an unvented reaction cavity. We designed and characterized valves ranging in centrifugal burst pressure from 6700 Pa to 2100 Pa. Based on this valving principle we present a new structure for aliquoting of liquids. We experimentally demonstrated this by splitting 105 muL volumes into 16 aliquots with a volume CV of 3 %
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