14 research outputs found
Pervasive gaps in Amazonian ecological research
Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4
While the increasing availability of global databases on ecological communities has advanced our knowledge
of biodiversity sensitivity to environmental changes,5–7 vast areas of the tropics remain understudied.8–11 In
the American tropics, Amazonia stands out as the world’s most diverse rainforest and the primary source of
Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13–15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazon’s biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus
crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced
environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian
Amazonia, while identifying the region’s vulnerability to environmental change. 15%–18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by
2050. This means that unless we take immediate action, we will not be able to establish their current status,
much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio
Pervasive gaps in Amazonian ecological research
Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost
Alternative hyperspherical adiabatic decoupling scheme for tetratomic molecules: quantum two-dimensional study of the ammonia umbrella motion
The prototypical example of the inversion of ammonia is studied as an approach to
hyperspheric decoupling schemes for tetratomic molecule. We perform two-dimensional
calculations including totally symmetric stretching and inversion modes, associated to the
hyperradius and an hyperangle. Two adiabatic procedures are employed: the hyperradial one
where the hyperangular part is solved to give hyperradial adiabatic curves, and the
hyperangular one where the hyperradial part is solved to give hyperangular adiabatic
curves. Two methodologies are employed: the hyperquantization algorithm and the finite
element method. For completeness a diabatic procedure is also formulated
Umbrella motion of the methyl cation, radical, and anion molecules
The main purpose of the present work is to characterize the umbrella inversion motion of
the CH-3, CH3 and CH-3 molecules as a function of the environmental
conditions. In particular, for the three investigated species we have studied how
temperature affects times for umbrella inversion modes and their propagation velocity.
These data are used to predict the statistical behavior of the reactions involving the
AB3 like
molecules and to relate the umbrella potential with the rate constants. The second aspect
of this study concerns the molecular distribution charges as a function of the umbrella
opening angle and of the total charge. The results have been used to calculate the induced
electric field on a probe charge located at a given position perpendicular to the plane of
the hydrogen atoms which is the most relevant for the reaction. Obtained values are
presented as a function of the umbrella opening angle
Umbrella motion of the methyl cation, radical, and anion molecules
A study of the umbrella motion of the methyl cation, radical, and anion molecules is
presented. This is the floppiest mode of vibration of all three species and its
characterization is of fundamental importance for understanding their reactivity. Minimum
Energy Paths of the umbrella motions according to the hyperspherical treatment were
obtained, by single point calculations, at the CCSD(T)/aug-cc-pVQT level of theory in the
Born-Oppenheimer approximation. These energy profiles permit us to calculate the
vibrational levels through the Hyperquantization algorithm, which is shown appropriated
for the description of the umbrella motion of these three molecules. The adiabatic
electron affinity and ionization potentials were estimated to good accuracy. Partition
functions are also calculated in order to obtain information on the reaction rates
involving these groups
Couplings and recouplings of four angular momenta: Alternative 9j symbols and spin addition diagrams
Quantum angular momentum, projective geometry and the networks of seven and ten spins: Fano, Desargues and alternative incidence configurations
The basic ingredients of the quantum theory of orbital and spin angular momentum (vector coefficients,
3nj symbols) encounter continuing relevance in wide areas beyond the traditional ones (molecular,
atomic and nuclear spectroscopies and dynamics). This paper offers insight on the connection at the most
elementary of levels with the diagrammatic approaches to projective geometry. In particular here we
exhibit how the Fano, Desargues and related incidence configurations emerge in the Racah and in the
Biedenharn-Elliott identities, corresponding respectively to the hexagonal and pentagonal relationships
that provide the basis for the construction of 3nj symbols and of spin networks. It is shown that the treatment,
although mostly confined to the quadrangulation of the real projective plane, permits however the
introduction of networks involving seven and ten spins, and preludes to developments towards computational
and asymptotic approaches for quantum and semi-classical applications to spectroscopy and
dynamics