2,143 research outputs found
Termination of (many) 4-dimensional log flips
We prove that any sequence of 4-dimensional log flips that begins with a klt
pair (X,D) such that -(K+D) is numerically equivalent to an effective divisor,
terminates. This implies termination of flips that begin with a log Fano pair
and termination of flips in a relative birational setting. We also prove
termination of directed flips with big K+D. As a consequence, we prove
existence of minimal models of 4-dimensional dlt pairs of general type,
existence of 5-dimensional log flips, and rationality of Kodaira energy in
dimension 4.Comment: 13 pages; a minor change in the proof of Thm.4.
Extending Torelli map to toroidal compactifications of Siegel space
It has been known since the 1970s that the Torelli map ,
associating to a smooth curve its jacobian, extends to a regular map from the
Deligne-Mumford compactification to the 2nd Voronoi
compactification .
We prove that the extended Torelli map to the perfect cone (1st Voronoi)
compactification is also regular, and moreover
and share a common Zariski open
neighborhood of the image of . We also show that the map to the
Igusa monoidal transform (central cone compactification) is NOT regular for
; this disproves a 1973 conjecture of Namikawa.Comment: To appear in Inventiones Mathematica
Anti-Pluricanonical Systems On Q-Fano Threefolds
We investigate birationality of the anti-pluricanonical map , the
rational map defined by the anti-pluricanonical system , on
-Fano threefolds.Comment: 18 page
Preimaginal Stages of the Emerald Ash Borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae): An Invasive Pest on Ash Trees (Fraxinus)
This study provides the most detailed description of the immature stages of Agrilus planipennis Fairmaire to date and illustrates suites of larval characters useful in distinguishing among Agrilus Curtis species and instars. Immature stages of eight species of Agrilus were examined and imaged using light and scanning electron microscopy. For A. planipennis all preimaginal stages (egg, instars I-IV, prepupa and pupa) were described. A combination of 14 character states were identified that serve to identify larvae of A. planipennis. Our results support the segregation of Agrilus larvae into two informal assemblages based on characters of the mouthparts, prothorax, and abdomen: the A. viridis and A. ater assemblages, with A. planipennis being more similar to the former. Additional evidence is provided in favor of excluding A. planipennis from the subgenus Uragrilus
Biases in Variance of Decomposed Portfolio Returns
Significant portfolio variance biases arise when contrasting multiperiod portfolio returns based on the assumption of fixed continuously rebalanced portfolio weights as opposed to buy‐and‐hold weights. Empirical evidence obtained using S&P 500 constituents from 2003 to 2011 demonstrates that, compared with a buy‐and‐hold assumption, applying fixed weights led to decreased estimates of portfolio volatilities during 2003, 2005 and 2010, but caused a significant increase in volatility estimates in the more turbulent 2008 and 2011. This discrepancy distorts assessments of portfolio risk‐adjusted performance when inappropriate weight assumptions are employed. Consequently, these variance biases have effect on statistical inference in factor models and may result in erroneous portfolio size recommendations for adequate diversification
Fano threefolds of large Fano index and large degree
We classify Q-Fano threefolds of Fano index > 2 and big degree.Comment: 38 page
Asymptotically cylindrical 7-manifolds of holonomy G_2 with applications to compact irreducible G_2-manifolds
We construct examples of exponentially asymptotically cylindrical Riemannian
7-manifolds with holonomy group equal to G_2. To our knowledge, these are the
first such examples. We also obtain exponentially asymptotically cylindrical
coassociative calibrated submanifolds. Finally, we apply our results to show
that one of the compact G_2-manifolds constructed by Joyce by desingularisation
of a flat orbifold T^7/\Gamma can be deformed to one of the compact
G_2-manifolds obtainable as a generalized connected sum of two exponentially
asymptotically cylindrical SU(3)-manifolds via the method given by the first
author (math.DG/0012189).Comment: 36 pages; v2: corrected trivial typos; v3: some arguments corrected
and improved; v4: a number of improvements on presentation, paritularly in
sections 4 and 6, including an added picture
Риски в сфере оказания логистических услуг при транснациональных транспортировках
Риски в сфере оказания логистических услуг при транснациональных транспортировках необходимо идентифицировать и минимизировать на стадии подготовки товарной партии к транспортировке; освещены этапы организации транснациональных транспортировок и возникающие на каждом этапе риски, а также способы их минимизации; проанализирована судебная практика для определения наиболее распространённых видов риска при оказании логистических услуг.Risks in the field of providing logistic services for transnational transportation should be identified and minimized at the stage of preparation of the goods lot for transportation; the stages of organization of transnational transportation and the risks arising at each stage, as well as ways to minimize them, are covered; the court practice is analyzed to determine the most common types of risk in the provision of logistics services
A generalized Tullock contest
We construct a generalized Tullock contest under complete information where contingent upon winning or losing, the payoff of a player is a linear function of prizes, own effort, and the effort of the rival. This structure nests a number of existing contests in the literature and can be used to analyze new types of contests. We characterize the unique symmetric equilibrium and show that small parameter modifications may lead to substantially different types of contests and hence different equilibrium effort levels
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