33,703 research outputs found
Trends in High Nature Value farmland studies: A systematic review
Background. Since the High Nature Value (HNV) concept was defined in the early 1990s, several studies on HNV farmland has been increasing over the past 30 years in Europe, highlighting the interest by scientific community of HNV farming systems supporting biodiversity conservation. The aim of this study was to evaluate the trends and main gaps on HNV farmland peer-reviewed publications in order to contribute to the effectiveness of future research in this field. Methods. Searches were conducted using the databases Web of SciencesTM and Scopus in order to identify only peer-reviewed articles on HNV farmland, published prior to July 2017. The inclusion and exclusion criteria were developed a priori. Data as year, country, type of document, subject area, taxa studied and biodiversity metrics assessed were extracted and explored in order to analyse the spatial and temporal distribution of the concept, including the main topics addressed in HNV farmland literature. Results. After screening 308 original articles, 90 were selected for this review. HNV farmland studies involved several disciplines, mainly biodiversity and conservation and environmental sciences and ecology. Most peer-reviewed articles focused on HNV farming were conducted in Spain, Italy, Ireland and Portugal. The main studied taxa were plants and birds. Taxonomic diversity was the biodiversity metric more often used to assess the biodiversity status on HNV farmland areas. A positive correlation was found between HNV farmland area and HNV farmland studies conducted in respective countries. Discussion. The HNV farmland research subject is a relative novel approach, and this systematic review provides a comprehensive overview about the main topics in the HNV farmland peer-reviewed literature contributing to highlight the main gaps and provide some considerations in order to assist the performance of HNV farming systems and conservation policies, addressed to sustain high levels of biodiversity
On ideal triangulations of surfaces up to branched transit equivalences
We consider triangulations of closed surfaces S with a given set of vertices
V; every triangulation can be branched that is enhanced to a Delta-complex.
Branched triangulations are considered up to the b-transit equivalence
generated by b-flips (i.e. branched diagonal exchanges) and isotopy keeping V
point-wise fixed. We extend a well known connectivity result for `naked'
triangulations; in particular in the generic case when S has negative
Euler-Poincare' characteristic c(S), we show that branched triangulations are
equivalent to each other if c(S) is even, while this holds also for odd c(S)
possibly after the complete inversion of one of the two branchings. Moreover we
show that under a mild assumption, two branchings on a same triangulation are
connected via a sequence of inversions of ambiguous edges (and possibly the
total inversion of one of them). A natural organization of the b-flips in
subfamilies gives rise to restricted transit equivalences with non trivial
(even infinite) quotient sets. We analyze them in terms of certain preserved
structures of differential topological nature carried by any branched
triangulations; in particular a pair of transverse foliations with determined
singular sets contained in V, including as particular cases the configuration
of the vertical and horizontal foliations of the square of an Abelian
differential on a Riemann surface.Comment: 22 pages, 11 figure
Critical behavior in spherical and hyperbolic spaces
We study the effects of curved background geometries on the critical behavior
of scalar field theory. In particular we concentrate on two maximally symmetric
spaces: -dimensional spheres and hyperboloids. In the first part of the
paper, by applying the Ginzburg criterion, we find that for large correlation
length the Gaussian approximation is valid on the hyperboloid for any dimension
, while it is not trustable on the sphere for any dimension. This is
understood in terms of various notions of effective dimension, such as the
spectral and Hausdorff dimension. In the second part of the paper, we apply
functional renormalization group methods to develop a different perspective on
such phenomena, and to deduce them from a renormalization group analysis. By
making use of the local potential approximation, we discuss the consequences of
having a fixed scale in the renormalization group equations. In particular, we
show that in the case of spheres there is no true phase transition, as symmetry
restoration always occurs at large scales. In the case of hyperboloids, the
phase transition is still present, but as the only true fixed point is the
Gaussian one, mean field exponents are valid also in dimensions lower than
four.Comment: 24 pages, 5 figures; several improvements in the presentation and
small corrections, 2 figures adde
On the number of relevant operators in asymptotically safe gravity
The asymptotic safety scenario of gravity conjectures that (i) the quantum
field theory of gravity exists thanks to the presence of a non-trivial
ultraviolet fixed point of the renormalization group, and that (ii) the fixed
point has only a finite number of relevant perturbations, i.e. a finite number
of UV-stable directions (or in other words, a finite number of free parameters
to be fixed experimentally). Within the f(R) approximation of the functional
renormalization group equation of gravity, we show that assuming the first half
of the conjecture to be true, the remaining half follows from general
arguments, that is, we show that assuming the existence of a non-trivial fixed
point, the fact that the number of relevant directions is finite is a general
consequence of the structure of the equations.Comment: 5 pages; v3: one typo corrected (thanks to Juergen Dietz for pointing
it out
Ideal triangulations of 3-manifolds up to decorated transit equivalences
We consider 3-dimensional pseudo-manifolds M with a given set of marked point
V such that M-V is the interior of a compact 3-manifold with boundary. An ideal
triangulation T of (M, V ) has V as its set of vertices. A branching (T, b)
enhances T to a Delta-complex. Branched triangulations of (M, V ) are
considered up to the b-transit equivalence generated by isotopy and ideal
branched moves which keep V pointwise fixed. We extend a well known
connectivity result for naked triangulations by showing that branched ideal
triangulations of (M, V) are equivalent to each other. A pre-branching is a
system of transverse orientations at the 2-facets of T verifying a certain
global constraint; pre-branchings are considered up to a natural pb-transit
equivalence. If M is oriented, every branching b induces a pre-branching w(b)
and every b-transit induces a pb-transit. The quotient set of pre-branchings up
to transit equivalence is far to be trivial; we get some information about it
and we characterize the pre-branchings of type w(b). Pre-branched and branched
moves are naturally organized in subfamilies which give rise to restricted
transit equivalences. In the branching setting we revisit early results about
the sliding transit equivalence and outline a conceptually different approach
to the branched connectivity and eventually also to the naked one. The basic
idea is to point out some structures of differential topological nature which
are carried by every branched ideal triangulation, are preserved by the sliding
transits and can be modified by the whole branched transits. The non ambiguous
transit equivalence already widely studied on pre-branchings lifts to a
specialization of the sliding equivalence on branchings; we point out a few
specific insights, again in terms of carried structures preserved by the non
ambiguous and which can be modified by the whole sliding transits.Comment: 29 pages, 22 figure
Collapses, products and LC manifolds
Durhuus and Jonsson (1995) introduced the class of "locally constructible"
(LC) triangulated manifolds and showed that all the LC 2- and 3-manifolds are
spheres. We show here that for each d>3 some LC d-manifolds are not spheres. We
prove this result by studying how to collapse products of manifolds with
exactly one facet removed.Comment: 6 pages; added references; minor changes. Accepted for J. Comb.
Theory, Series
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