259 research outputs found
Can forest structural diversity be a response to anthropogenic stress? A case study in old-growth fir Abies alba Mill. stands
International audienceAbstractKey messageFrom 1973 to 1991, Polish SO2emissions above 3250 Gg/year resulted in a decline of firAbies albaMill. After stresses connected with these emissions, five main diameter at breast height (DBH) structural types were described. This type of heterogeneous forest structure is supposed to increase forest resistance and resilience to abiotic, biotic and anthropogenic disturbances.ContextThe analyses of forest structure are important under the current scenario of global change, since heterogeneous structures allow for better responses to disturbances. Forests with more complex structures should present greater vitality.AimsThe main hypotheses were as follows: (1) the temporal changes of atmospheric SO2 emissions caused (a) the abrupt changes in the tree DBH radial increment and (b) the death of fir trees; and (2) atmospheric SO2 emissions and related fir decline and recovery processes ultimately result in the development of stands characterised by diverse DBH structures.MethodsRadial growth trends of 49 and 215 fir trees in the older and younger generations, respectively, and 85 dead fir trees were evaluated. Using data collected in 32 stands, the DBH structural types were identified, and the shapes of these types were illustrated.ResultsThe structural diversification of forest patches may influence forest resistance and resilience to disturbances; five main structural types were identified: ML1 and ML2 represent DBH distributions of multi-layered stands, and OS, TS1 and TS2 represent DBH distributions of one- and two-storied stands.ConclusionStructural diversity of forests was a response to SO2 emissions; fir trees had the ability to increase their radial growth, although there were still high SO2 emissions
Tendencje w europejskim i polskim wyższym szkolnictwie rolniczym
In most European countries the number of students taking agricultural courses will continue to decline. In Poland, however, the arrival of new agricultural courses in public vocational schools of higher education as well as in private schools of higher education will lead to a gradual increase in the number of students studying agriculture. In “old” European countries as well as in Poland individuals who choose agricultural studies will have fewer job opportunities. In the USA and in Europę narrowly-defined technological agricultural education is clearly being abandoned in favour of education in natural resources protection and rural development management. In Poland, however, this process is barely noticeable, particularly in traditional agricultural departments. In the short-term, agricultural schools of higher education should modify their organisation, curricula and the teaching processes, otherwise they will face gradual exclusion from the global tertiary agricultural education system.W większości krajów europejskich liczba studentów kierunków rolniczych będzie ulegać zmniejszeniu. W Polsce natomiast - dzięki otwieraniu nowych kierunków rolniczych zarówno w państwowych wyższych szkołach zawodowych, jak i w uczelniach niepublicznych - liczba studentów szeroko rozumianych kierunków rolniczych będzie się stopniowo zwiększać. Zarówno w krajach „starej” Unii Europejskiej, jak i w Polsce wybór kierunków rolniczych będzie skutkował osiąganiem mniejszych możliwości samorealizacji w życiu zawodowym. W Stanach Zjednoczonych i w Europie następuje wyraźne odejście od wąsko pojętego, technologicznego kształcenia rolniczego w stronę kształcenia w zakresie ochrony zasobów naturalnych (natural resources) oraz zarządzania rozwojem obszarów wiejskich (rural development management). W Polsce ten proces jest słabo zauważalny, zwłaszcza na tradycyjnych wydziałach rolniczych. W najbliższej przyszłości uczelnie rolnicze powinny zmodyfikować swoją organizację, programy studiów i sposób realizacji procesu dydaktycznego. Jeśli tego nie uczynią, będą stopniowo wyłączane z globalnego kształcenia rolniczego na poziomie wyższym
Idempotents of Clifford Algebras
A classification of idempotents in Clifford algebras C(p,q) is presented. It
is shown that using isomorphisms between Clifford algebras C(p,q) and
appropriate matrix rings, it is possible to classify idempotents in any
Clifford algebra into continuous families. These families include primitive
idempotents used to generate minimal one sided ideals in Clifford algebras.
Some low dimensional examples are discussed
Results on system size dependence of strangeness production in the CERN SPS energy range from NA61/SHINE
NA61/SHINE is a multipurpose fixed-target facility at the CERN Super Proton
Synchrotron. The main goals of the NA61/SHINE strong interactions program are
to discover the critical point of strongly interacting matter and study the
properties of the onset of deconfinement. To reach these goals, hadron
production measurements are performed in the form of a two-dimensional scan by
varying collision energy and system size. The Collaboration has recently
finished data acquisition for its original program on strong interactions,
accumulating broad data samples on hadron production in various systems in the
SPS energy range.\\ In this contribution, the NA61/SHINE results on identified
charged kaon and pion production in p+p, Be+Be and Ar+Sc collisions at the SPS
energy range (=5.1--17.3 GeV) are presented. The NA61/SHINE
measurements of small and intermediate-mass ion collisions establish an
interesting system size dependence, showing a rapid change of hadron production
properties that starts when moving from Be+Be to Ar+Sc system. In particular,
Ar+Sc is the smallest system for which a significant enhancement of
ratio with respect to + collisions is observed. Obtained energy and
system size dependence of the measured charged hadron multiplicities are
compared with available world data and various theoretical models
Approximating nonlinear functions with latent boundaries in low-rank excitatory-inhibitory spiking networks
Deep feedforward and recurrent rate-based neural networks have become
successful functional models of the brain, but they neglect obvious biological
details such as spikes and Dale's law. Here we argue that these details are
crucial in order to understand how real neural circuits operate. Towards this
aim, we put forth a new framework for spike-based computation in low-rank
excitatory-inhibitory spiking networks. By considering populations with rank-1
connectivity, we cast each neuron's spiking threshold as a boundary in a
low-dimensional input-output space. We then show how the combined thresholds of
a population of inhibitory neurons form a stable boundary in this space, and
those of a population of excitatory neurons form an unstable boundary.
Combining the two boundaries results in a rank-2 excitatory-inhibitory (EI)
network with inhibition-stabilized dynamics at the intersection of the two
boundaries. The computation of the resulting networks can be understood as the
difference of two convex functions, and is thereby capable of approximating
arbitrary non-linear input-output mappings. We demonstrate several properties
of these networks, including noise suppression and amplification, irregular
activity and synaptic balance, as well as how they relate to rate network
dynamics in the limit that the boundary becomes soft. Finally, while our work
focuses on small networks (5-50 neurons), we discuss potential avenues for
scaling up to much larger networks. Overall, our work proposes a new
perspective on spiking networks that may serve as a starting point for a
mechanistic understanding of biological spike-based computation
The recursive scheme of clustering
The problem of data clustering is one of the most important in data analysis.
It can be problematic when dealing with experimental data characterized by
measurement uncertainties and errors. Our paper proposes a recursive scheme for
clustering data obtained in geographical (climatological) experiments. The
discussion of results obtained by k-means and SOM methods with the developed
recursive procedure is presented. We show that the clustering using the new
approach gives more acceptable results when compared to experts assessments
Samogłoska y w językach słowiańskich: geneza i ewolucja (przegląd)
The article concerns the origin and development of the Slavic vowel *y in Slavic languages. At the starting point I present the articulatory characteristics of contemporary Polish y, and then move on to the late Indo-European vocal system - the primordial source of the discussed sound. Then I move on to the analysis of the circumstances of the creation of the phoneme y including phonetics - delabialisation *ū1, and phonology - change *ū1 → y as a consequence of the creation of ū2 from the monophthongisation of diphthongs. I also present the views of researchers on the old pronunciation of y. In the main part of the article I focus on the analysis of the occurrence and functioning of y in various Slavic languages, including dialects, without losing sight of the accompanying historical perspectiv
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