Showing papers by "Stockholm University published in 2001"

Catastrophic shifts in ecosystems.

Abstract: All ecosystems are exposed to gradual changes in climate, nutrient loading, habitat fragmentation or biotic exploitation. Nature is usually assumed to respond to gradual change in a smooth way. However, studies on lakes, coral reefs, oceans, forests and arid lands have shown that smooth change can be interrupted by sudden drastic switches to a contrasting state. Although diverse events can trigger such shifts, recent studies show that a loss of resilience usually paves the way for a switch to an alternative state. This suggests that strategies for sustainable management of such ecosystems should focus on maintaining resilience.

The causes of land-use and land-cover change: moving beyond the myths

Abstract: Common understanding of the causes of land-use and land-cover change is dominated by simplifications which, in turn, underlie many environment-development policies. This article tracks some of the major myths on driving forces of land-cover change and proposes alternative pathways of change that are better supported by case study evidence. Cases reviewed support the conclusion that neither population nor poverty alone constitute the sole and major underlying causes of land-cover change worldwide. Rather, peoples’ responses to economic opportunities, as mediated by institutional factors, drive land-cover changes. Opportunities and

The web of human sexual contacts

Abstract: This article analyses data gathered in a 1996 Swedish survey of sexual behavior of 4781 Swedes aged 18-74 years. The authors state that the most important finding is the scale-free nature of the connectivity of an objectively defined non-professional social network. The possibility that the web of sexual contacts has a scale-free structure indicates that strategic targeting of safe-sex education campaigns t o those individuals with a large number of partners may significantly reduce the propagation of sexually transmitted diseases.

The Web of Human Sexual Contacts

Abstract: Many ``real-world'' networks are clearly defined while most ``social'' networks are to some extent subjective. Indeed, the accuracy of empirically-determined social networks is a question of some concern because individuals may have distinct perceptions of what constitutes a social link. One unambiguous type of connection is sexual contact. Here we analyze data on the sexual behavior of a random sample of individuals, and find that the cumulative distributions of the number of sexual partners during the twelve months prior to the survey decays as a power law with similar exponents $\alpha \approx 2.4$ for females and males. The scale-free nature of the web of human sexual contacts suggests that strategic interventions aimed at preventing the spread of sexually-transmitted diseases may be the most efficient approach.

Is There a Glass Ceiling in Sweden

Abstract: Using data from 1998, we show that the gender log wage gap in Sweden increases throughout the wage distribution and accelerates in the upper tail of the distribution, which we interpret as a glass ceiling effect. Using earlier data, we show that the same pattern held at the beginning of the 1990's but not in the prior two decades. Further, we do not find this pattern either for the log wage gap between immigrants and non-immigrants in the Swedish labor market or for the gender gap in the U.S. labor market. Our findings suggest that a gender-specific mechanism in the Swedish labor market hinders women from reaching the top of the wage distribution. Using quantile regressions, we examine whether this pattern can be asribed primarily to gender differences in labor market characteristics or to gender differences in rewards to those characteristics. We estimate pooled quantile regressions with gender dummies, as well as separate quantile regressions by gender, and we carry out a decomposition analysis in the spirit of the Oaxaca-Blinder technique. Even after extensive controls for gender differences in age, education (both level and field), sector, industry, and occupation, we find that the glass ceiling effect we see in the raw data persists to a considerable extent.

The Indian Ocean Experiment: Widespread Air Pollution from South and Southeast Asia

Abstract: The Indian Ocean Experiment (INDOEX) was an international, multiplatform field campaign to measure long-range transport of air pollution from South and Southeast Asia toward the Indian Ocean during the dry monsoon season in January to March 1999. Surprisingly high pollution levels were observed over the entire northern Indian Ocean toward the Intertropical Convergence Zone at about 6°S. We show that agricultural burning and especially biofuel use enhance carbon monoxide concentrations. Fossil fuel combustion and biomass burning cause a high aerosol loading. The growing pollution in this region gives rise to extensive air quality degradation with local, regional, and global implications, including a reduction of the oxidizing power of the atmosphere.

Electoral Rules and Corruption

Abstract: Is corruption systematically related to electoral rules? A number of studies have tried to uncover economic and social determinants of corruption but, as far as we know, nobody has yet empirically investigated how electoral systems influence corruption. We try to address this lacuna in the literature, by relating corruption to different features of the electoral system in a sample from the late nineties encompassing more than 80 (developed and developing) democracies. Our empirical results are based on traditional regression methods, as well as non-parametric estimators. The evidence is consistent with the theoretical models reviewed in the Paper. Holding constant a variety of economic and social variables, we find that larger voting districts - and thus lower barriers to entry - are associated with less corruption, whereas larger shares of candidates elected from party lists - and thus less individual accountability - are associated with more corruption. Altogether, proportional elections are associated with more corruption, since voting over party lists is the dominant effect, while the district magnitude effect is less robust.

Local Ecological Knowledge and Institutional Dynamics for Ecosystem Management: A Study of Lake Racken Watershed, Sweden

Abstract: The sustainable use of resources requires that management practices and institutions take into account the dynamics of the ecosystem. In this paper, we explore the role of local ecological knowledge and show how it is used in management practices by a local fishing association in a contemporary rural Swedish community. We focus on the local management of crayfish, a common-pool resource, and also address the way crayfish management is linked to institutions at different levels of Swedish society. Methods from the social sciences were used for information gathering, and the results were analyzed within the framework of ecosystem management. We found that the practices of local fishing association resemble an ecosystem approach to crayfish management. Our results indicate that local users have substantial knowledge of resource and ecosystem dynamics from the level of the individual crayfish to that of the watershed, as reflected in a variety of interrelated management practices embedded in and influenced by institutions at several levels. We propose that this policy of monitoring at several levels simultaneously, together with the interpretation of a bundle of indicators and associated management responses, enhances the possibility of building ecological resilience into the watershed. Furthermore, we found that flexibility and adaptation are required to avoid command-and-control pathways of resource management. We were able to trace the development of the local fishing association as a response to crisis, followed by the creation of an opportunity for reorganization and the recognition of slow ecosystem structuring variables, and also to define the role of knowledgeable individuals in the whole process. We discuss the key roles of adaptive capacity, institutional learning, and institutional memory for successful ecosystem management and conclude that scientific adaptive management could benefit from a more explicit collaboration with flexible community-based systems of resource management for the implementation of policies as experiments.

Evolution of cooperation through indirect reciprocity

Abstract: How can cooperation through indirect reciprocity evolve and what would it be like? This problem has previously been studied by simulating evolution in a small group of interacting individuals, assuming no gene flow between groups. In these simulations, certain 'image scoring' strategies were found to be the most successful. However, analytical arguments show that it would not be in an individual's interest to use these strategies. Starting with this puzzle, we investigate indirect reciprocity in simulations based on an island model. This has an advantage in that the role of genetic drift can be examined. Our results show that the image scoring strategies depend on very strong drift or a very small cost of giving help. As soon as these factors are absent, selection eliminates image scoring. We also consider other possibilities for the evolution of indirect reciprocity. In particular, we find that the strategy of aiming for 'good standing' has superior properties. It can be an evolutionarily stable strategy and, even if not, it usually beats image scoring. Furthermore, by introducing quality variation among individuals into the model, we show that the standing strategy can be quality revealing, adding a new dimension to indirect reciprocity. Finally, we discuss general problems with currently popular modelling styles.

Integrating seaweeds into marine aquaculture systems: a key toward sustainability

Abstract: The rapid development of intensive fed aquaculture (e.g. finfish and shrimp) throughout the world is associated with concerns about the environmental impacts of such often monospecific practices, especially where activities are highly geographically concentrated or located in suboptimal sites whose assimilative capacity is poorly understood and, consequently, prone to being exceeded. One of the main environmental issues is the direct discharge of significant nutrient loads into coastal waters from open-water systems and with the effluents from land-based systems. In its search for best management practices, the aquaculture industry should develop innovative and responsible practices that optimize its efficiency and create diversification, while ensuring the remediation of the consequences of its activities to maintain the health of coastal waters. To avoid pronounced shifts in coastal processes, conversion, not dilution, is a common-sense solution, used for centuries in Asian countries. By integrating fed aquaculture (finfish, shrimp) with inorganic and organic extractive aquaculture (seaweed and shellfish), the wastes of one resource user become a resource (fertilizer or food) for the others. Such a balanced ecosystem approach provides nutrient bioremediation capability, mutual benefits to the cocultured organisms, economic diversification by producing other value-added marine crops, and increased profitability per cultivation unit for the aquaculture industry. Moreover, as guidelines and regulations on aquaculture effluents are forthcoming in several countries, using appropriately selected seaweeds as renewable biological nutrient scrubbers represents a cost-effective means for reaching compliance by reducing the internalization of the total environmental costs. By adopting integrated polytrophic practices, the aquaculture industry should find increasing environmental, economic, and social acceptability and become a full and sustainable partner within the development of integrated coastal management frameworks.

The Weak Temperature Gradient Approximation and Balanced Tropical Moisture Waves

Abstract: Horizontal temperature gradients are small in the tropical atmosphere, as a consequence of the smallness of the Coriolis parameter near the equator. This provides a strong constraint on both large-scale fluid dynamics and diabatic processes. This work is a step toward the construction of a balanced dynamical theory for the tropical circulation that is based on this constraint, and in which the diabatic processes are explicit and interactive. The authors first derive the basic fluid-dynamical scaling under the weak temperature gradient (WTG) approximation in a shallow water system with a fixed mass source representing an externally imposed heating. This derivation follows an earlier similar one by Held and Hoskins, but extends the analysis to the nonlinear case (though on an f plane), examines the resulting system in more detail, and presents a solution for an axisymmetric ‘‘top-hat’’ forcing. The system is truly balanced, having no gravity waves, but is different from other balance models in that the heating is included a priori in the scaling. The WTG scaling is then applied to a linear moist model in which the convective heating is controlled by a moisture variable that is advected by the flow. This moist model is derived from the Quasi-equilibrium Tropical Circulation Model (QTCM) equations of Neelin and Zeng but can be viewed as somewhat more general. A number of additional approximations are made in order to consider balanced dynamical modes, apparently not studied previously, which owe their existence to interactions of the moisture and flow fields. A particularly interesting mode arises on an f plane with a constant background moisture gradient. In the limit of low frequency and zero meridional wavenumber this mode has a dispersion relation mathematically identical to that of a barotropic Rossby wave, though the phase speed is eastward (for moisture decreasing poleward in the background state) and the propagation mechanism is quite different. This mode also has significant positive growth rate for low wavenumbers. The addition of the b effect complicates matters. For typical parameters, when b is included the direction of phase propagation is ambiguous, and the growth rate reduced, as the effects of the background gradients in moisture and planetary vorticity appear to cancel to a large degree. Possible relevance to intraseasonal variability and easterly wave dynamics is briefly discussed.

Likelihood-based cointegration tests in heterogeneous panels

Abstract: Summary This paper presents a maximum likelihood panel test of the cointegrating rank in heterogeneous panel models based on the mean of the individual rank trace statistics. The existence of the first two moments of the asymptotic distribution of the individual trace statistic is established. Based on this, the asymptotic distribution of the test statistic is shown to be normal. The small-sample size and power properties are investigated using Monte Carlo simulations. An empirical example for a consumption model including consumption, income and inflation is estimated for 23 OECD countries over the period 1960-1994. The results indicate that two cointegrating relations exist in the system: one containing consumption and income and one inflation only.

Social taboos: “invisible” systems of local resource management and biological conservation

Abstract: Social taboos exist in most cultures, both Western and non-Western. They are good examples of informal institutions, where norms, rather than governmental juridical laws and rules, determine human behavior. In many traditional societies throughout the world, taboos frequently guide human conduct toward the natural environment. Based on a survey of recent literature, we synthesize information on such taboos. We refer to them as “resource and habitat taboos” (RHTs). Examples are grouped in six different categories depending on their potential nature conservation and management functions. We compare RHTs with contemporary measures of conservation and identify and discuss some key benefits that may render them useful in partnership designs for conservation and management. We conclude that many RHTs have functions similar to those of formal institutions for nature conservation in contemporary society but have not been sufficiently recognized in this capacity. We suggest that designs for conservation of biologi...

Flame retardants in indoor air at an electronics recycling plant and at other work environments.

Abstract: Air samples from a plant engaged in recycling electronics goods, a factory assembling printed circuit boards, a computer repair facility, offices equipped with computers, and outdoor air have been analyzed with respect to their content of brominated hydrocarbon and phosphate ester flame retardants. Polybrominated diphenyl ethers, polybrominated biphenyls, 1,2-bis(2,4,6-tribromophenoxy)-ethane, tetrabromobisphenol A, and organophosphate esters were all detected in the indoor air samples, with the highest concentrations being detected in air from the recycling plant. In air from the dismantling hall at the recycling plant the average concentrations of decabromodiphenyl ether, tetrabromobisphenol A, and triphenyl phosphate were 38, 55, and 58 pmol/m3, respectively. Significantly higher levels of all of these additives were present in air in the vicinity of the shredder at the dismantling plant. This is the first time that 1,2-bis(2,4,6-tribromophenoxy)-ethane and several arylated phosphate esters are reported to be contaminants of air in occupational settings. At all of the other sites investigated, low levels of flame retardants were detected in the indoor air. Flame retardants associated with airborne particles, present at elevated levels, pose a potential health hazard to the exposed workers.

Towards artificial photosynthesis: ruthenium–manganese chemistry for energy production

Abstract: The synthesis and characterisation of supramolecular model systems mimicking the light reactions on the donor side of Photosystem II (PSII) in green plants have been reviewed In these systems, manganese complexes and tyrosine are electron donors, modelling the manganese cluster and tyrosineZ in PSII The donors have been covalently linked to a photosensitizer, a ruthenium(II) tris-bipyridyl complex, that plays the role of the P680 chlorophylls in PSII It has been demonstrated that, in the presence of an external electron acceptor in solution, the model systems can undergo an intermolecular electron transfer from the photoexcited state of RuII to an acceptor, followed by an intramolecular electron transfer from the coordinated Mn complexes or the tyrosine unit to the photogenerated RuIII This leads to regeneration of the RuII and oxidation of the Mn complexes or generation of a tyrosine radical The process closely mimics the primary reaction steps on the donor side of PSII

Spatial Resilience of Coral Reefs

Abstract: There have been several earlier studies that addressed the influence of natural disturbance regimes on coral reefs. Humans alter natural disturbance regimes, introduce new stressors, and modify background conditions of reefs. We focus on how coral reef ecosystems relate to disturbance in an increasingly human-dominated environment. The concept of ecosystem resilience—that is, the capacity of complex systems with multiple stable states to absorb disturbance, reorganize, and adapt to change—is central in this context. Instead of focusing on the recovery of certain species and populations within disturbed sites of individual reefs, we address spatial resilience—that is, the dynamic capacity of a reef matrix to reorganize and maintain ecosystem function following disturbance. The interplay between disturbance and ecosystem resilience is highlighted. We begin the identification of spatial sources of resilience in dynamic seascapes and exemplify and discuss the relation between “ecological memory” (biological legacies, mobile link species, and support areas) and functional diversity for seascape resilience. Managing for resilience in dynamic seascapes not only enhances the likelihood of conserving coral reefs, it also provides insurance to society by sustaining essential ecosystem services.

Currency unions and trade: how large is the treatment effect?

Abstract: Currency unions and trade What can the data say? The impact of a common currency on trade can be grossly mismeasured if countries that belong to currency unions are systematically different from those that do not, and if the relationship between trade and its observable determinants is complex. I argue that such complications are plausible and likely to distort the empirical results of a recent Economic Policy paper by Andrew Rose (Issue 30, 2000: pp. 7–45). Using techniques designed to be robust in this situation, I find that the effects of common currency on international trade are considerably less dramatic and much less precisely estimated. — Torsten persson I have always maintained that the measured effect of a single currency on trade appears implausibly large, but I am not convinced by Torsten Persson’s diagnosis and proposed solution. I apply a variety of estimation techniques to a new larger data set, where many more instances of currency union creation and abandonment make it possible to rely on time–series as well as cross–sectional evidence. The results are similar to my earlier ones: the effect of a single currency on trade is large. — Andrew Rose

Stringy gravity, interacting tensionless strings and massless higher spins

Abstract: Consequences of a strong version of the AdS/CFT correspondence for extremely stringy physics are examined. In particular, properties of N = 4 supersymmetric Yang-Mills theory are used to extract results about interacting tensionless strings and massless higher spin fields in an AdS5 × S5 background. Furthermore, the thermodynamics of this model signals the presence of a Hawking-Page phase transition between AdS5 space and a “black hole”-like high temperature configuration even in the extreme string limit.

Widespread Origins of Domestic Horse Lineages

Abstract: Domestication entails control of wild species and is generally regarded as a complex process confined to a restricted area and culture. Previous DNA sequence analyses of several domestic species have suggested only a limited number of origination events. We analyzed mitochondrial DNA (mtDNA) control region sequences of 191 domestic horses and found a high diversity of matrilines. Sequence analysis of equids from archaeological sites and late Pleistocene deposits showed that this diversity was not due to an accelerated mutation rate or an ancient domestication event. Consequently, high mtDNA sequence diversity of horses implies an unprecedented and widespread integration of matrilines and an extensive utilization and taming of wild horses. However, genetic variation at nuclear markers is partitioned among horse breeds and may reflect sex-biased dispersal and breeding.

Racemisation in asymmetric synthesis. Dynamic kinetic resolution and related processes in enzyme and metal catalysis

Abstract: Dynamic kinetic resolution (DKR) has recently become not only an alternative to the traditional kinetic resolution, but also a new procedure for asymmetric synthesis. Enzymes are usually the tools to effect this methodology (DKR), although new techniques have emerged through the use of asymmetric transition metal catalysis. All of these methods need two supplementary steps: racemisation together with a consecutive asymmetric transformation. A breakthrough in this area appeared with the powerful combination of enzymatic resolution and transition metal-catalysed racemisation. Thus, new procedures for efficient dynamic kinetic resolution became available. This review covers the concept of dynamic kinetic resolutions emphasizing the most representative examples as well as new developments in this area. Special effort has been made to show the importance of the racemisation step in the whole asymmetric transformation process.

Physical characterization of aerosol particles during nucleation events

Abstract: Particle concentrations and size distributions have been measured from different heights inside and above a boreal forest during three BIOFOR campaigns (14 April–22 May 1998, 27 July–21 August 1998 and 20 March–24 April 1999) in Hyytiala, Finland Typically, the shape of the background distribution inside the forest exhibited 2 dominant modes: a fine or Aitken mode with a geometric number mean diameter of 44 nm and a mean concentration of 1160 cm −3 and an accumulation mode with mean diameter of 154 nm and a mean concentration of 830 cm −3 A coarse mode was also present, extending up to sizes of 20 μm having a number concentration of 12 cm −3 , volume mean diameter of 20 μm and a geometric standard deviation of 19 Aerosol humidity was lower than 50% during the measurements Particle production was observed on many days, typically occurring in the late morning Under these periods of new particle production, a nucleation mode was observed to form at diameter of the order of 3 nm and, on most occasions, this mode was observed to grow into Aitken mode sizes over the course of a day Total concentrations ranged from 410–45 000 cm −3 , the highest concentrations occurring on particle production days A clear gradient was observed between particle concentrations encountered below the forest canopy and those above, with significantly lower concentrations occurring within the canopy Above the canopy, a slight gradient was observed between 18 m and 67 m, with at maximum 5% higher concentration observed at 67 m during the strongest concentration increases DOI: 101034/j1600-08892001530403x

Timescale stretch parameterization of Type Ia supernova B-band light curves

Abstract: R-band intensity measurements along the light curve of Type Ia supernovae discovered by the Cosmology Project (SCP) are fitted in brightness to templates allowing a free parameter the time-axis width factor w identically equal to s times (1+z). The data points are then individually aligned in the time-axis, normalized and K-corrected back to the rest frame, after which the nearly 1300 normalized intensity measurements are found to lie on a well-determined common rest-frame B-band curve which we call the composite curve. The same procedure is applied to 18 low-redshift Calan/Tololo SNe with Z < 0.11; these nearly 300 B-band photometry points are found to lie on the composite curve equally well. The SCP search technique produces several measurements before maximum light for each supernova. We demonstrate that the linear stretch factor, s, which parameterizes the light-curve timescale appears independent of z, and applies equally well to the declining and rising parts of the light curve. In fact, the B band template that best fits this composite curve fits the individual supernova photometry data when stretched by a factor s with chi 2/DoF ~;~; 1, thus as well as any parameterization can, given the current data sets. The measurement of the data of explosion, however, is model dependent and not tightly constrained by the current data. We also demonstrate the 1 + z light-cure time-axis broadening expected from cosmological expansion. This argues strongly against alternative explanations, such as tired light, for the redshift of distant objects.

Segregation of nitrogen fixation and oxygenic photosynthesis in the marine cyanobacterium Trichodesmium.

Abstract: In the modern ocean, a significant amount of nitrogen fixation is attributed to filamentous, nonheterocystous cyanobacteria of the genus Trichodesmium. In these organisms, nitrogen fixation is confined to the photoperiod and occurs simultaneously with oxygenic photosynthesis. Nitrogenase, the enzyme responsible for biological N2 fixation, is irreversibly inhibited by oxygen in vitro. How nitrogenase is protected from damage by photosynthetically produced O2 was once an enigma. Using fast repetition rate fluorometry and fluorescence kinetic microscopy, we show that there is both temporal and spatial segregation of N2 fixation and photosynthesis within the photoperiod. Linear photosynthetic electron transport protects nitrogenase by reducing photosynthetically evolved O2 in photosystem I (PSI). We postulate that in the early evolutionary phase of oxygenic photosynthesis, nitrogenase served as an electron acceptor for anaerobic heterotrophic metabolism and that PSI was favored by selection because it provided a micro-anaerobic environment for N2 fixation in cyanobacteria.

Hurwitz numbers and intersections on moduli spaces of curves

Abstract: 1 Department of Mathematics, University of Stockholm, S-10691, Stockholm, Sweden (e-mail: teke@matematik.su.se) 2 Higher College of Mathematics, Independent University of Moscow and Institute for System Research RAS, Moscow, Russia (e-mail: lando@mccme.ru) 3 Department of Mathematics, Royal Institute of Technology, S-10044, Stockholm, Sweden (e-mail: mshapiro@math.kth.se) 4 Department of Mathematics and Department of Computer Science, University of Haifa, Haifa 31905, Israel (e-mail: alek@mathcs.haifa.ac.il)