Stockholm University

About: Stockholm University is a education organization based out in Stockholm, Sweden. It is known for research contribution in the topics: Population & Context (language use). The organization has 21052 authors who have published 62567 publications receiving 2725859 citations. The organization is also known as: University of Stockholm & Stockholms universitet.

Coupled Human and Natural Systems

Abstract: Humans have continuously interacted with natural systems, resulting in the formation and development of coupled human and natural systems (CHANS). Recent studies reveal the complexity of organizational, spatial, and temporal couplings of CHANS. These couplings have evolved from direct to more indirect interactions, from adjacent to more distant linkages, from local to global scales, and from simple to complex patterns and processes. Untangling complexities, such as reciprocal effects and emergent properties, can lead to novel scientific discoveries and is essential to developing effective policies for ecological and socioeconomic sustainability. Opportunities for truly integrating various disciplines are emerging to address fundamental questions about CHANS and meet society's unprecedented challenges.

Perturbation of the northern hemisphere radiative balance by backscattering from anthropogenic sulfate aerosols

Abstract: Anthropogenic sulfate (SO 4 = ) aerosol particles play two potential roles in the radiative climate of the earth. In cloud-free air, SO 4 = particles scatter sunlight, some of which is lost to space, thereby reducing solar irradiance at the ground. The same particles can act as cloud condensation nuclei (CCN), the number concentration of which is an important determinant of cloud albedo. This albedo effect, in turn, also influences incoming short-wave solar radiation. Development of a three-dimensional global model for estimating the SO 4 = aerosol mass concentration, along with previously-acquired information on the scattering and back-scattering coefficients per unit mass concentration allow calculation of the effects of anthropogenic SO 4 = aerosol on clear-sky optical depth. Subsequently, this can be used to estimate the change in hemispheric and global average reflected solar radiation. The conclusion is that the change of reflected solar flux due to anthropogenic SO 4 = averaged over the Northern Hemisphere is ca. − 1.1 Wm -2 , which is comparable but opposite in sign to the present-day radiative forcing by anthropogenic CO 2 , + 1.5 Wm -2 . Because of the spatial variability of the anthropogenic SO 4 = distribution, its meteorological effects must be studied regionally. That is, global models with regional resolution and regional data are required. Unlike the direct effect on solar irradiance, the relationship of CCN number concentration to mass concentration is not known. Thus it is not yet possible to make quantitatively reliable statements about anthropogenic forcing of cloud albedo, although there is qualitative evidence that the CCN effect may also be substantial. DOI: 10.1034/j.1600-0870.1991.00013.x

Seed and microsite limitation of recruitment in plant populations.

Abstract: Availability of seed and microsites, respectively, are two factors that potentially may limit recruitment in plant populations. Microsites are small-scale sites suitable for germination and survival of seedlings. We discuss this dichotomy of recruitment limitation both from a theoretical and empirical point of view. Investigations of recruitment in 14 woodland species showed that 3 species were seed limited, 6 species were limited by a combination of seed and microsite availability, and 5 species were found not to be seed limited, but the limiting factor was not identified. A “combination of seed and microsite limitation” implies that recruitment is promoted by increasing both seed and microsite availability. We suggest that the importance of seed limitation in plant populations has been underestimated, and that the operating limiting factors may be dependent on spatial and temporal scale. We expect that many species, if adequately studied, will turn out to be both seed and microsite limited. Experimental field studies that incorporate a range of seed and microsite “densities” in various spatial and temporal scales are needed to examine the extent to which plant populations are seed and microsite limited.

Exceptional topology of non-Hermitian systems

Abstract: The current understanding of the role of topology in non-Hermitian (NH) systems and its far-reaching physical consequences observable in a range of dissipative settings are reviewed. In particular, how the paramount and genuinely NH concept of exceptional degeneracies, at which both eigenvalues and eigenvectors coalesce, leads to phenomena drastically distinct from the familiar Hermitian realm is discussed. An immediate consequence is the ubiquitous occurrence of nodal NH topological phases with concomitant open Fermi-Seifert surfaces, where conventional band-touching points are replaced by the aforementioned exceptional degeneracies. Furthermore, new notions of gapped phases including topological phases in single-band systems are detailed, and the manner in which a given physical context may affect the symmetry-based topological classification is clarified. A unique property of NH systems with relevance beyond the field of topological phases consists of the anomalous relation between bulk and boundary physics, stemming from the striking sensitivity of NH matrices to boundary conditions. Unifying several complementary insights recently reported in this context, a picture of intriguing phenomena such as the NH bulk-boundary correspondence and the NH skin effect is put together. Finally, applications of NH topology in both classical systems including optical setups with gain and loss, electric circuits, and mechanical systems and genuine quantum systems such as electronic transport settings at material junctions and dissipative cold-atom setups are reviewed.