Showing papers by "Stockholm University published in 1999"

Measurements of Omega and Lambda from 42 High-Redshift Supernovae

Abstract: We report measurements of the mass density, Omega_M, and cosmological-constant energy density, Omega_Lambda, of the universe based on the analysis of 42 Type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these SNe, at redshifts between 0.18 and 0.83, are fit jointly with a set of SNe from the Calan/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. All SN peak magnitudes are standardized using a SN Ia lightcurve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8 Omega_M - 0.6 Omega_Lambda ~= -0.2 +/- 0.1 in the region of interest (Omega_M <~ 1.5). For a flat (Omega_M + Omega_Lambda = 1) cosmology we find Omega_M = 0.28{+0.09,-0.08} (1 sigma statistical) {+0.05,-0.04} (identified systematics). The data are strongly inconsistent with a Lambda = 0 flat cosmology, the simplest inflationary universe model. An open, Lambda = 0 cosmology also does not fit the data well: the data indicate that the cosmological constant is non-zero and positive, with a confidence of P(Lambda > 0) = 99%, including the identified systematic uncertainties. The best-fit age of the universe relative to the Hubble time is t_0 = 14.9{+1.4,-1.1} (0.63/h) Gyr for a flat cosmology. The size of our sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We find no significant differences in either the host reddening distribution or Malmquist bias between the low-redshift Calan/Tololo sample and our high-redshift sample. The conclusions are robust whether or not a width-luminosity relation is used to standardize the SN peak magnitudes.

ChloroP, a neural network-based method for predicting chloroplast transit peptides and their cleavage sites.

Abstract: We present a neural network based method (ChloroP) for identifying chloroplast transit peptides and their cleavage sites. Using cross-validation, 88% of the sequences in our homology reduced training set were correctly classified as transit peptides or nontransit peptides. This performance level is well above that of the publicly available chloroplast localization predictor PSORT. Cleavage sites are predicted using a scoring matrix derived by an automatic motif-finding algorithm. Approximately 60% of the known cleavage sites in our sequence collection were predicted to within +/-2 residues from the cleavage sites given in SWISS-PROT. An analysis of 715 Arabidopsis thaliana sequences from SWISS-PROT suggests that the ChloroP method should be useful for the identification of putative transit peptides in genome-wide sequence data. The ChloroP predictor is available as a web-server at http://www.cbs.dtu.dk/services/ChloroP/.

Challenging Theophrastus: A common core list of plant traits for functional ecology

Abstract: . Ecologists need a common language of plant traits in order to make comparisons across regions and scales, pool data, and maximize the utility of the data. To develop such a set of traits we began with the primary challenges faced by plants: dispersal, establishment, and persistence in order to identify fundamental traits. Most of these traits are hard to measure, but advances in comparative ecology have suggested a number of easy to measure analogs. Unfortunately, some of the fundamental traits have no simple analog. The common core list includes: seed mass, seed shape, dispersal mode, clonality, specific leaf area, leaf water content, height, above-ground biomass, life history, onset of flowering, stem density, and resprouting ability. Most of the traits can be measured quantitatively, but several traits on the list must still be measured qualitatively due to logistical problems or lack of an easy analog. Key problem areas include: dispersal ability, capacity for vegetative spread, germination, palatability, plasticity, and all the various below-ground traits. Comparative studies need to address these problem areas. The common core list is suggested as a common starting point for studies of functional ecology. The idiosyncrasies of regional floras and specific research agendas will dictate which traits can be ignored and those that need to be added.

Social Norms and Economic Incentives in the Welfare State

Abstract: This paper analyzes the interplay between social norms and economic incentives in the context of work decisions in the modern welfare state. We assume that to live off one's own work is a social no ...

Transient climate change simulations with a coupled atmosphere–ocean GCM including the tropospheric sulfur cycle

Abstract: The time-dependent climate response to changing concentrations of greenhouse gases and sulfate aerosols is studied using a coupled general circulation model of the atmosphere and the ocean (ECHAM4/OPYC3). The concentrations of the well-mixed greenhouse gases like CO2, CH4, N2O, and CFCs are prescribed for the past (1860–1990) and projected into the future according to International Panel on Climate Change (IPCC) scenario IS92a. In addition, the space–time distribution of tropospheric ozone is prescribed, and the tropospheric sulfur cycle is calculated within the coupled model using sulfur emissions of the past and projected into the future (IS92a). The radiative impact of the aerosols is considered via both the direct and the indirect (i.e., through cloud albedo) effect. It is shown that the simulated trend in sulfate deposition since the end of the last century is broadly consistent with ice core measurements, and the calculated radiative forcings from preindustrial to present time are within th...

Impact of climatic change on the northern latitude limit and population density of the disease-transmitting European tick Ixodes ricinus.

Abstract: We examined whether a reported northward expansion of the geographic distribution limit of the disease-transmitting tick Ixodes ricinus and an increased tick density between the early 1980s and mid...

The Inhibitor of Death Receptor Signaling, Flice-Inhibitory Protein Defines a New Class of Tumor Progression Factors

Abstract: Death receptor–mediated apoptosis can be modulated by several antiapoptotic proteins, such as the FLICE (FADD [Fas-associated death domain]-like IL-1β–converting enzyme)-inhibitory proteins (FLIPs) The FLIP family includes both cellular and viral members The Kaposi's sarcoma–associated herpesvirus protein (KSHV)-FLIP is expressed by human herpesvirus 8 (HHV-8), which is associated with malignancies such as Kaposi's sarcoma and certain lymphomas In this paper, we demonstrate that KSHV-FLIP protects cells from Fas-mediated apoptosis by inhibiting caspase activation and permits clonal growth in the presence of death stimuli in vitro Furthermore, we show that KSHV-FLIP can act as a tumor progression factor by promoting tumor establishment and growth in vivo When injected into immunocompetent recipient mouse strains, murine B lymphoma cells (A20) transduced with KSHV-FLIP rapidly develop into aggressive tumors showing a high rate of survival and growth The tumor-progressive activity of KSHV-FLIP is mediated by prevention of death receptor–induced apoptosis triggered by conventional T cells Consequently, inhibitors of death receptor signaling can be regarded as a new class of tumor progression factors, and HHV-8–associated tumors may represent naturally occurring examples of the tumorigenic effect of such inhibitors

Dimensions of the Precautionary Principle

Abstract: This essay attempts to provide an analytical apparatus which may be used for finding an authoritative formulation1 of the Precautionary Principle. Several formulations of the Precautionary Principle are examined. Four dimensions of the principle are identified: (1) the threat dimension, (2) the uncertainty dimension, (3) the action dimension, and (4) the command dimension. It is argued that the Precautionary Principle can be recast into the following if-clause, containing these four dimensions: “If there is (1) a threat, which is (2) uncertain, then (3) some kind of action (4) is mandatory.” The phrases expressing these dimensions may vary in (a) precision and (b) strength. It is shown that it is the dimension containing the weakest phrase that determines the strength of the entire principle. It is suggested that the four-dimensional if-clause be used as an analytical apparatus in negotiations of the Precautionary Principle.

Flame retardant exposure: polybrominated diphenyl ethers in blood from Swedish workers.

Abstract: Polybrominated diphenyl ethers (PBDEs) are used as additives in polymers and textiles to prohibit the development of fires. Because of the production and use of PBDEs, their lipophilic characteristics, and persistence, these compounds have become ubiquitous environmental contaminants. The aim of the present study was to determine potential exposures of PBDEs to clerks working full-time at computer screens and personnel at an electronics-dismantling plant, with hospital cleaners as a control group. Five PBDE congeners--2,2´,4,4´-tetraBDE ; 2,2´,4,4´,5,5´-hexaBDE ; 2,2´,4,4´,5,6´-hexaBDE ; 2,2´,3,4,4´,5´,6-heptaBDE ; and decaBDE--were quantified in blood serum from all three categories of workers. Subjects working at the dismantling plant showed significantly higher levels of all PBDE congeners in their serum as compared to the control group. Decabromodiphenyl ether is present in concentrations of 5 pmol/g lipid weight (lw) in the personnel dismantling electronics ; these concentrations are comparable to the concentrations of 2,2´,4,4´-tetraBDE. The latter compound was the dominating PBDE congener in the clerks and cleaners. The major compound in personnel at the dismantling plant was 2,2´,3,4,4´,5´,6-heptaBDE. Concentrations of this PBDE congener are almost twice as high as for 2,2´,4,4´-tetraBDE in these workers and seventy times the level of this heptaBDE in cleaners. The total median PBDE concentrations in the serum from workers at the electronics-dismantling plant, clerks, and cleaners were 37, 7.3, and 5.4 pmol/g lw, respectively. The results show that decabromodiphenyl ether is bioavailable and that occupational exposure to PBDEs occurs at the electronics-dismantling plant.

Betwixt and between: Temporary Employees as Liminal Subjects in Flexible Organizations

Abstract: As organizations change to become more flexible and transient, the use of a flexible workforce becomes an attractive solution. Temporary employees are here tentatively viewed as being `betwixt and between' organizational structures, in transit between the relatively fixed positions of full-time, regular employment. Building on previous fieldwork and recent interviews among temporary employees in Sweden and the US, the notion of liminality is employed to explore aspects of temporary work. The liminal position of `temporaries', it is suggested, is an ambiguous position involving both risks and opportunities for individuals, temporary staffing agencies, and client organizations alike. It may be seen as a seedbed of cultural creativity, where old perspectives on work and subjectivity are contested and new ones created. Related to the transient, mobile character of temporary employment, is an enhanced awareness of substitutability and a continuous reflexive monitoring of manners and competencies. Furthermore, ...

Frozen-bed Fennoscandian and Laurentide ice sheets during the Last Glacial Maximum

Abstract: The areal extents of the Laurentide and Fennoscandian ice sheets during the Last Glacial Maximum (about 20,000 years ago) are well known1, but thickness estimates range widely, from high-domed2 to thin3, with large implications for our reconstruction of the climate system regarding, for example, Northern Hemisphere atmospheric circulation and global sea levels. This uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials4, a knowledge of which would better constrain reconstructions of ice-sheet thickness. Here we show that, in the absence of direct data, the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen- and thawed-bed conditions. We argue that ribbed moraines were formed by brittle fracture of subglacial sediments, induced by the excessive stress at the boundary between frozen- and thawed-bed conditions resulting from the across-boundary difference in basal ice velocity. Maps of glacial landforms from aerial photographs of Canada and Scandinavia reveal a concentration of ribbed moraines around the ice-sheet retreat centres of Quebec, Keewatin, Newfoundland and west-central Fennoscandia. Together with the evidence from relict landscapes that mark glacial areas with frozen-bed conditions, the distribution of ribbed moraines on both continents suggest that a large area of the Laurentide and Fennoscandian ice sheets was frozen-based—and therefore high-domed and stable—during the Last Glacial Maximum.

Tropical climates at the Last Glacial Maximum: a new synthesis of terrestrial palaeoclimate data. I. Vegetation, lake-levels and geochemistry

Abstract: Palaeodata in synthesis form are needed as benchmarks for the Palaeoclimate Modelling Intercomparison Project (PMIP). Advances since the last synthesis of terrestrial palaeodata from the last glacial maximum (LGM) call for a new evaluation, especially of data from the tropics. Here pollen, plant-macrofossil, lake-level, noble gas (from groundwater) and δ18O (from speleothems) data are compiled for 18±2 ka (14C), 32 °N–33 °S. The reliability of the data was evaluated using explicit criteria and some types of data were re-analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month (MTCO), mean annual temperature (MAT), plant available moisture (PAM) and runoff (P-E). Cold-month temperature (MAT) anomalies from plant data range from −1 to −2 K near sea level in Indonesia and the S Pacific, through −6 to −8 K at many high-elevation sites to −8 to −15 K in S China and the SE USA. MAT anomalies from groundwater or speleothems seem more uniform (−4 to −6 K), but the data are as yet sparse; a clear divergence between MAT and cold-month estimates from the same region is seen only in the SE USA, where cold-air advection is expected to have enhanced cooling in winter. Regression of all cold-month anomalies against site elevation yielded an estimated average cooling of −2.5 to −3 K at modern sea level, increasing to ≈−6 K by 3000 m. However, Neotropical sites showed larger than the average sea-level cooling (−5 to −6 K) and a non-significant elevation effect, whereas W and S Pacific sites showed much less sea-level cooling (−1 K) and a stronger elevation effect. These findings support the inference that tropical sea-surface temperatures (SSTs) were lower than the CLIMAP estimates, but they limit the plausible average tropical sea-surface cooling, and they support the existence of CLIMAP-like geographic patterns in SST anomalies. Trends of PAM and lake levels indicate wet LGM conditions in the W USA, and at the highest elevations, with generally dry conditions elsewhere. These results suggest a colder-than-present ocean surface producing a weaker hydrological cycle, more arid continents, and arguably steeper-than-present terrestrial lapse rates. Such linkages are supported by recent observations on freezing-level height and tropical SSTs; moreover, simulations of “greenhouse” and LGM climates point to several possible feedback processes by which low-level temperature anomalies might be amplified aloft.

Methodological aspects of life cycle assessment of integrated solid waste management systems

Abstract: Environmental life cycle assessment (LCA) developed rapidly during the 1990s and has reached a certain level of harmonisation and standardisation. LCA has mainly been developed for analysing material products, but can also be applied to services, e.g. treatment of a particular amount of solid waste. This paper discusses some methodological issues which come into focus when LCAs are applied to solid waste management systems. The following five issues are discussed. (1) Upstream and downstream system boundaries: where is the ‘cradle’ and where is the ‘grave’ in the analysed system? (2) Open-loop recycling allocation: besides taking care of a certain amount of solid waste, many treatment processes also provide additional functions, e.g. energy or materials which are recycled into other products. Two important questions which arise are if an allocation between the different functions should be made (and if so how), or if system boundaries should be expanded to include several functions. (3) Multi-input allocation: in waste treatment processes, different materials and products are usually mixed. In many applications there is a need to allocate environmental interventions from the treatment processes to the different input materials. The question is how this should be done. (4) Time: emissions from landfills will continue for a long time. An important issue to resolve is the length of time emissions from the landfill should be considered. (5) Life cycle impact assessment: are there any aspects of solid waste systems (e.g. the time horizon) that may require specific attention for the impact assessment element of an LCA? Although the discussion centres around LCA it is expected that many of these issues are also relevant for other types of systems analyses.

Competition between Sec- and TAT-dependent protein translocation in Escherichia coli.

Abstract: Recently, a new protein translocation pathway, the twin-arginine translocation (TAT) pathway, has been identified in both bacteria and chloroplasts. To study the possible competition between the TAT- and the well-characterized Sec translocon-dependent pathways in Escherichia coli, we have fused the TorA TAT-targeting signal peptide to the Sec-dependent inner membrane protein leader peptidase (Lep). We find that the soluble, periplasmic P2 domain from Lep is re-routed by the TorA signal peptide into the TAT pathway. In contrast, the full-length TorA-Lep fusion protein is not re-routed into the TAT pathway, suggesting that Sec-targeting signals in Lep can override TAT-targeting information in the TorA signal peptide. We also show that the TorA signal peptide can be converted into a Sec-targeting signal peptide by increasing the hydrophobicity of its h-region. Thus, beyond the twin-arginine motif, the overall hydrophobicity of the signal peptide plays an important role in TAT versus Sec targeting. This is consistent with statistical data showing that TAT-targeting signal peptides in general have less hydrophobic h-regions than Sec-targeting signal peptides.

Metal Availability and Bioconcentration in Plants

Abstract: Heavy metals are natural elements that are found at various high background levels (Table 1.1) at different places throughout the world, due to various concentrations in the bedrock. Thus, for example, Ni, Cr and Co are abundant in serpentine soils whereas Zn, Pb and Cd are high in calamine soils. Heavy metals are persistent and cannot be deleted from the environment. Thus, a problem arises when their availability is high due to high background levels or to human activity.

Price Level Targeting vs. Inflation Targeting: A Free Lunch?

Abstract: Price level targeting (without base drift) and inflation targeting (with base drift) are compared under commitment and discretion, with persistence in unemployment. Price level targeting is often said to imply more short-run inflation variability and thereby more employment variability than inflation targeting. Counter to this conventional wisdom, under discretion a price level target results in lower inflation variability than an inflation target (if unemployment is at least moderately persistent). A price level target also eliminates the inflation bias under discretion and, as is well known, reduces long-term price variability. Society may be better off assigning a price level target to the central bank even if its preferences correspond to inflation targeting. A price level target thus appears to have more advantages than commonly acknowledged.

Dietary Uptake and Biological Effects of Decabromodiphenyl Ether in Rainbow Trout (Oncorhynchus mykiss)

Abstract: Dietary uptake and biological effects of decabromodiphenyl ether in the rainbow trout (Oncorhynchus mykiss)

Manganese Oxyl Radical Intermediates and O−O Bond Formation in Photosynthetic Oxygen Evolution and a Proposed Role for the Calcium Cofactor in Photosystem II

Abstract: Spin state considerations are proposed to sharply limit the possible O−O bond-forming steps in water oxidation by the oxygen evolving center of Photosystem II. A series of intermediates are proposed for the Kok S states on the basis of quantum chemical studies on simple model complexes; these are also consistent with the main biophysical data. Only one Mn atom in the active site cluster is thought to be redox-active and mediate O−O bond formation. A key concept is the formation of an unreactive MnO oxo at the S2 state, followed by its conversion to a reactive Mn−O• oxyl form at the S3 level, with radical character on the oxyl oxygen, at which point O−O bond formation can occur by a coupling between the oxyl and an outer-sphere water molecule. An MnOOH intermediate at S3 is proposed to lose a hydrogen atom to give O2. The role of the Ca cofactor is to bring about a 5- to 6-coordination change at S2, necessary for formation of a reactive oxo in S3. The chloride cofactor is assigned the role of charge neutra...

Inflation Targeting: Some Extensions

Abstract: Previous analyses of the implementation of inflation targeting are extended to monetary policy responses to different shocks, consequences of model uncertainty, and effects of interest rate smoothing and stabilization Model uncertainty, output stabilization, and interest rate stabilization or smoothing all call for a more gradual adjustment of the conditional inflation forecast toward the inflation target The conditional inflation forecast is the natural intermediate target during inflation targeting The optimal way of reacting to shocks is hence to check how they affect the inflation forecast and then take the appropriate action