530 research outputs found
Atmospheric Chemistry of Organic Sulfur and Nitrogen Compounds. 1. Annual Progress Report 1988 (EV4V-0067-C)
Deformation independent open brane metrics and generalized theta parameters
We investigate the consequences of generalizing certain well established
properties of the open string metric to the conjectured open membrane and open
Dp-brane metrics. By imposing deformation independence on these metrics their
functional dependence on the background fields can be determined including the
notorious conformal factor. In analogy with the non-commutativity parameter
in the string case, we also obtain `generalized' theta
parameters which are rank q+1 antisymmetric tensors (polyvectors) for open
Dq-branes and rank 3 for the open membrane case. The expressions we obtain for
the open membrane quantities are expected to be valid for general background
field configurations, while the open D-brane quantities are only valid for one
parameter deformations. By reducing the open membrane data to five dimensions,
we show that they, modulo a subtlety with implications for the relation between
OM-theory and NCYM, correctly generate the open string and open D2-data.Comment: 24 pages, LaTe
Narrow genetic base in forest restoration with holm oak (Quercus ilex L.) in Sicily
In order to empirically assess the effect of actual seed sampling strategy on
genetic diversity of holm oak (Quercus ilex) forestations in Sicily, we have
analysed the genetic composition of two seedling lots (nursery stock and
plantation) and their known natural seed origin stand by means of six nuclear
microsatellite loci. Significant reduction in genetic diversity and significant
difference in genetic composition of the seedling lots compared to the seed
origin stand were detected. The female and the total effective number of
parents were quantified by means of maternity assignment of seedlings and
temporal changes in allele frequencies. Extremely low effective maternity
numbers were estimated (Nfe 2-4) and estimates accounting for both
seed and pollen donors gave also low values (Ne 35-50). These values
can be explained by an inappropriate forestry seed harvest strategy limited to
a small number of spatially close trees
Diverse Beliefs and Time Variability of Risk Premia
Why do risk premia vary over time? We examine this problem theoretically and empirically by studying the effect of market belief on risk premia. Individual belief is taken as a fundamental primitive state variable. Market belief is observable; it is central to the empirical evaluation and we show how to measure it. Our asset pricing model is familiar from the noisy REE literature but we adapt it to an economy with diverse beliefs. We derive equilibrium asset prices and implied risk premium. Our approach permits a closed form solution of prices; hence we trace the exact effect of market belief on the time variability of asset prices and risk premia. We test empirically the theoretical conclusions. Our main result is that, above the effect of business cycles on risk premia, fluctuations in market belief have significant independent effect on the time variability of risk premia. We study the premia on long positions in Federal Funds Futures, 3- and 6-month Treasury Bills (T-Bills). The annual mean risk premium on holding such assets for 1-12 months is about 40-60 basis points and we find that, on average, the component of market belief in the risk premium exceeds 50% of the mean. Since time variability of market belief is large, this component frequently exceeds 50% of the mean premium. This component is larger the shorter is the holding period of an asset and it dominates the premium for very short holding returns of less than 2 months. As to the structure of the premium we show that when the market holds abnormally favorable belief about the future payoff of an asset the market views the long position as less risky hence the risk premium on that asset declines. More generally, periods of market optimism (i.e. "bull" markets) are shown to be periods when the market risk premium is low while in periods of pessimism (i.e. "bear" markets) the market's risk premium is high. Fluctuations in risk premia are thus inversely related to the degree of market optimism about future prospects of asset payoffs. This effect is strong and economically very significant
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