4,273 research outputs found
Achieving New Upper Bounds for the Hypergraph Duality Problem through Logic
The hypergraph duality problem DUAL is defined as follows: given two simple
hypergraphs and , decide whether
consists precisely of all minimal transversals of (in which case
we say that is the dual of ). This problem is
equivalent to deciding whether two given non-redundant monotone DNFs are dual.
It is known that non-DUAL, the complementary problem to DUAL, is in
, where
denotes the complexity class of all problems that after a nondeterministic
guess of bits can be decided (checked) within complexity class
. It was conjectured that non-DUAL is in . In this paper we prove this conjecture and actually
place the non-DUAL problem into the complexity class which is a subclass of . We here refer to the logtime-uniform version of
, which corresponds to , i.e., first order
logic augmented by counting quantifiers. We achieve the latter bound in two
steps. First, based on existing problem decomposition methods, we develop a new
nondeterministic algorithm for non-DUAL that requires to guess
bits. We then proceed by a logical analysis of this algorithm, allowing us to
formulate its deterministic part in . From this result, by
the well known inclusion , it follows
that DUAL belongs also to . Finally, by exploiting
the principles on which the proposed nondeterministic algorithm is based, we
devise a deterministic algorithm that, given two hypergraphs and
, computes in quadratic logspace a transversal of
missing in .Comment: Restructured the presentation in order to be the extended version of
a paper that will shortly appear in SIAM Journal on Computin
The effects of enhanced Z penguins on lepton polarizations in
The sensitivity of the mode to electroweak penguins and the
recent experimental data for the , modes has given rise
to what is known as the `` puzzle''. Recently it has been observed
that this {\sl puzzle} can be resolved by considering the new physics which can
enter via penguins. In this note we analyze the effect of this enhanced
penguins on the lepton polarization asymmetries of .Comment: Published versio
The Hard X-ray emission of the blazar PKS 2155--304
The synchrotron peak of the X-ray bright High Energy Peaked Blazar (HBL) PKS
2155304 occurs in the UV-EUV region and hence its X-ray emission (0.6--10
keV) lies mostly in the falling part of the synchrotron hump. We aim to study
the X-ray emission of PKS 2155304 during different intensity states in
20092014 using XMMNewton satellite. We studied the spectral curvature of
all of the observations to provide crucial information on the energy
distribution of the non-thermal particles. Most of the observations show
curvature or deviation from a single power-law and can be well modeled by a log
parabola model. In some of the observations, we find spectral flattening after
6 keV. In order to find the possible origin of the X-ray excess, we built the
Multi-band Spectral Energy distribution (SED). We find that the X-ray excess in
PKS 2155--304 is difficult to fit in the one zone model but, could be easily
reconciled in the spine/layer jet structure. The hard X-ray excess can be
explained by the inverse Comptonization of the synchrotron photons (from the
layer) by the spine electrons.Comment: 14 pages, 7 Figures, Accepted for publication in Ap
Intermediation and Value Creation in an Incomplete Market: Implications for Securitization
This paper studies the impact of financial innovations on real investment decisions. We model an incomplete market economy comprised of firms, investors and an intermediary. The firms face unique investment opportunities that are not spanned by the traded securities in the financial market, and thus, cannot be priced uniquely using the no-arbitrage principle. The specific innovation we consider is securitization; the intermediary buys claims from the firms that are fully backed by cash flows from the new projects, pools these claims together, and then issues tranches of secondary securities to the investors. We first derive necessary and sufficient conditions under which pooling provides value enhancement and the prices paid to the firms are acceptable to them compared to the no-investment option or the option of forming alternative pools. We find that there is a unique pool that is sustainable, and may or may not consist of all projects in the intermediary’s consideration set.
We then determine the optimal design of tranches, fully backed by the asset pool, to be sold to different investor classes. We determine the general structure of the tranches. The new securities created by the intermediary could have up to three components, one that is a marketable claim, one that represents the arbitrage opportunities available in the market due to special ability to design and sell securities to a subset of investors, and a third component that is the rest of the asset pool which is sold at a price which does not exceed arbitrage based bounds to investors. The presence of these three components in the tranching solution has direct bearing upon the size of the asset pool, and therefore value creation due to financing additional projects
Intermediation and Value Creation in an Incomplete Market: Implications for Securitization
This paper studies the impact of financial innovations on real investment decisions. We
model an incomplete market economy comprised of firms, investors and an intermediary. The
firms face unique investment opportunities that are not spanned by the securities traded in the financial market, and thus, cannot be priced uniquely using the no-arbitrage principle. The specific innovation we consider is securitization: the intermediary buys claims from the firms that are fully backed by cash flows from the new projects, pools these claims together, and then issues tranches of secondary securities to the investors. We first derive necessary and
sufficient conditions under which pooling provides value enhancement from the new projects that are undertaken, and the prices paid to the firms are acceptable to them compared to the no-investment option or the option of forming alternative pools. We find that there is a unique pool that is sustainable, and which may or may not consist of all projects in the intermediary’s
consideration set
Spiders (Araneae) from Agricultural fields near foothill of Satpura Mountain ranges of Amravati District, Maharashtra, India.
This paper deals with the study of spider distribution in agricultural fields adjoining the Satpura Mountain Ranges of the Amravati district. The total collection of spiders comprises 12 families, 37 genera and 76 species. The Araneidae and Thomisidae families were dominant, followed by Saltisidae from the selected agricultural area. Lycosidae and Tetragnathidae were also found in a decreasing number of species due to their specific habitation. The analysis of guild structure revealed six feeding guilds. Orb web weavers and Ambushers constituted the dominant feeding guild representing 33% and 22% of the total collection respectively. Stalkers and ground runners represent 20% and 17% and foliage hunters and sheet web weavers represent 5% and 3% respectively. A new species of genus Sassacus (Beetle like spider), family Saltisidae was found for the first time in the Vidarbha region. The richness of spider diversity is a sign of the overall biodiversity which is a useful indicator of the species richness of the agro-ecosystem.

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