Declining labor force participation of older men throughout the 20th century and recent increases in participation have generated substantial interest in understanding the effect of public pensions on retirement. The National Bureau of Economic Research's International Social Security (ISS) Project, a long-term collaboration among researchers in a dozen developed countries, has explored this and related questions. The project employs a harmonized approach to conduct within-country analyses that are combined for meaningful cross-country comparisons. The key lesson is that the choices of policy makers affect the incentive to work at older ages and these incentives have important effects on retirement behavior.

The rapid growth of cultural evolutionary science, its expansion into numerous fields, its use of diverse methods, and several conceptual problems have outpaced corollary developments in theory and philosophy of science. This has led to concern, exemplified in results from a recent survey conducted with members of the Cultural Evolution Society, that the field lacks ‘knowledge synthesis’, is poorly supported by ‘theory’, has an ambiguous relation to biological evolution and uses key terms (e.g. ‘culture’, ‘social learning’, ‘cumulative culture’) in ways that hamper operationalization in models, experiments and field studies. Although numerous review papers in the field represent and categorize its empirical findings, the field's theoretical challenges receive less critical attention even though challenges of a theoretical or conceptual nature underlie most of the problems identified by Cultural Evolution Society members. Guided by the heterogeneous ‘grand challenges’ emergent in this survey, this paper restates those challenges and adopts an organizational style requisite to discussion of them. The paper's goal is to contribute to increasing conceptual clarity and theoretical discernment around the most pressing challenges facing the field of cultural evolutionary science. It will be of most interest to cultural evolutionary scientists, theoreticians, philosophers of science and interdisciplinary researchers.

Thwaites Glacier (TG) plays an important role in future sea-level rise (SLR) contribution from the West Antarctic Ice Sheet. Recent observations show that TG is losing mass, and its grounding zone is retreating. Previous modeling has produced a wide range of results concerning whether, when, and how rapidly further retreat will occur under continued warming. These differences arise at least in part from ill-constrained processes, including friction from the bed, and future atmosphere and ocean forcing affecting ice-shelf and grounding-zone buttressing. Here, we apply the Ice Sheet and Sea-level System Model (ISSM) with a range of specifications of basal sliding behavior in response to varying ocean forcing. We find that basin-wide bed character strongly affects TG's response to sub-shelf melt by modulating how changes in driving stress are balanced by the bed as the glacier responds to external forcing. Resulting differences in dynamic thinning patterns alter modeled grounding-line retreat across Thwaites' catchment, affecting both modeled rates and magnitudes of SLR contribution from this critical sector of the ice sheet. Bed character introduces large uncertainties in projections of TG under equal external forcing, pointing to this as a crucial constraint needed in predictive models of West Antarctica.

Predictions of marine ice-sheet behaviour require models able to simulate grounding-line migration. We present results of an intercomparison experiment for plan-view marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no buttressing effects from lateral drag). Perturbation experiments specifying spatial variation in basal sliding parameters permitted the evolution of curved grounding lines, generating buttressing effects. The experiments showed regions of compression and extensional flow across the grounding line, thereby invalidating the boundary layer theory. Steady-state grounding-line positions were found to be dependent on the level of physical model approximation. Resolving grounding lines requires inclusion of membrane stresses, a sufficiently small grid size (<500 m), or subgrid interpolation of the grounding line. The latter still requires nominal grid sizes of <5 km. For larger grid spacings, appropriate parameterizations for ice flux may be imposed at the grounding line, but the short-time transient behaviour is then incorrect and different from models that do not incorporate grounding-line parameterizations. The numerical error associated with predicting grounding-line motion can be reduced significantly below the errors associated with parameter ignorance and uncertainties in future scenarios.

We describe in detail the speed of `coming down from infinity' for birth-and-death processes which eventually become extinct. Under general assumptions on the birth-and-death rates, we firstly determine the behavior of the successive hitting times of large integers. We identify two different regimes depending on whether the mean time for the process to go from n+1 to n is negligible or not compared to the mean time to reach n from ∞. In the first regime, the coming down from infinity is very fast and the convergence is weak. In the second regime, the coming down from infinity is gradual and a law of large numbers and a central limit theorem for the hitting times sequence hold. By an inversion procedure, we deduce that the process is almost surely equivalent to a nonincreasing function when the time goes to 0. Our results are illustrated by several examples including applications to population dynamics and population genetics. The particular case where the death rate varies regularly is studied in detail.

Few studies have presented structural turnover models including both job satisfaction and organizational commitment measures. Recent research suggests that perceived supervisor leadership may contribute to employee well-being, job satisfaction and organizational commitment. This study proposes a structural turnover intention model including supervisory behavior (person-oriented and task-oriented dimensions), job satisfaction and organizational commitment. Furthermore, the study proposes to test whether this model fits in both small- and medium-sized enterprises and in large enterprises. The sample included 763 employees from different types of organizations who have completed a measure of their perception of their supervisor’s behavior and self-administrated measures of job satisfaction, organizational commitment and turnover intention. Results show that person-oriented leadership behavior affects turnover intentions through job satisfaction and organizational commitment more than task-oriented leadership behavior. Only organizational commitment had a direct effect in explaining turnover intention. Finally, results indicate that the model is applicable both in small- and medium-sized enterprises and large enterprises.

Agriculture in southern Greenland has a two-phase history: with the Norse, who first settled and farmed the region between 985ad and circa 1450ad, and with the recent reintroduction of sheep farming (1920ad to the present). The agricultural sector in Greenland is expected to grow over the next century as anticipated climate warming extends the length of the growing season and increases productivity. This article presents a synthesis of results from a well-dated 1500-year lake sediment record from Lake Igaliku, south Greenland (61°00′N, 45°26′W, 15m asl) that demonstrates the relative impacts of modern and Norse agricultural activities. Pollen, non-pollen palynomorphs (NPPs), sediment mass accumulation rates, diatoms and stable isotopes of nitrogen provide a comprehensive history of both phases of agriculture and their associated impacts on the landscape and adjacent lake. The initial colonisation of southern Greenland is marked by a loss of tree birch pollen, a rise in weed taxa, and an increase in coprophilous fungi and sediment accumulation rate consistent with land-use changes. The biological and chemical proxies within the lake, however, show only slight changes in diatom taxa, and a rise in δ15N. After the Norse demise and during the Little Ice Age, most of the markers return to pre-settlement conditions. However, the continuation of non-indigenous plant taxa suggests that the landscape did not completely return to a pre-disturbance state. After 1988, the character of the lake changed markedly: mesotrophic diatoms and N isotopes all reveal major shifts consistent with a trophic shift, together with a sharp rise in sediment accumulation rate. The post-1988 lake environment, affected by modern farming development, is unprecedented within the context of the last 1500 years. These results demonstrate the potential of lake sediment studies paired with archaeological investigations to reveal the relationship between climate, environment and human societies.

Heterodyne optical feedback on a class B laser is investigated for Scanning Near field Optical Microscopy (SNOM). All-fiberized set-up combining an Er-doped Distributed Feedback (DFB) fiber laser, a pair of pigtailed acousto-optics modulators (AOM) and a shear-force based scanning probe technique has been developed for the simultaneous observation of topography and evanescent light field on integrated optical devices. First demonstration of imaging using this technique is illustrated by characterizing the propagating modes into a rib waveguide at 1.54μm. Comparison between a theoretical model based on beam propagation mode (BPM) simulations and experimental measurements validates the results.

Tree nuts, peanuts and seeds are nutrient dense foods whose intake has been shown to be associated with reduced risk of some chronic diseases. They are regularly consumed in European diets either as whole, in spreads or from hidden sources (e.g. commercial products). However, little is known about their intake profiles or differences in consumption between European countries or geographic regions. The objective of this study was to analyse the population mean intake and average portion sizes in subjects reporting intake of nuts and seeds consumed as whole, derived from hidden sources or from spreads. Data was obtained from standardised 24-hour dietary recalls collected from 36 994 subjects in 10 different countries that are part of the European Prospective Investigation into Cancer and Nutrition (EPIC). Overall, for nuts and seeds consumed as whole, the percentage of subjects reporting intake on the day of the recall was: tree nuts = 4·4%, peanuts = 2·3% and seeds = 1·3%. The data show a clear northern (Sweden: mean intake = 0·15 g/d, average portion size = 15·1 g/d) to southern (Spain: mean intake = 2·99 g/d, average portion size = 34·7 g/d) European gradient of whole tree nut intake. The three most popular tree nuts were walnuts, almonds and hazelnuts, respectively. In general, tree nuts were more widely consumed than peanuts or seeds. In subjects reporting intake, men consumed a significantly higher average portion size of tree nuts (28·5 v. 23·1 g/d, P<0·01) and peanuts (46·1 v. 35·1 g/d, P<0·01) per day than women. These data may be useful in devising research initiatives and health policy strategies based on the intake of this food group.

The objective of this study is to assess and compare the relative impact of issues and the economy on the vote in democratic elections. There is a rich and vast literature dealing with issue voting and an equally impressive literature concerning economic voting. For the most part, however, these amount to two separate streams of research. Relatively little attention has been paid to where these literatures overlap and less still to the simple but basic question: which matters most, the issues or the economy?

The main debate in the issue voting literature recently has been between the directional and proximity models. That debate, engaging both technical and conceptual issues, has focused entirely on how issues play in an election, whether voters prefer the party that is closest to their own position or the party that is the strongest defender of their side on an issue. The question of how much issues affect the vote, however, has been neglected. Indeed, both the proximity and directional schools implicitly agree that issues matter, and so challenge the Michigan school's strong scepticism on the import of issues. Given that the difference between the two models is often quite small, a more fruitful line of investigation might be to return to the equally fundamental ‘how much’ question.

Scleroderris canker of conifer is caused by Gremmeniella abietina var. abietina, which comprises several taxa, including races, varieties, and biotypes. The European race of G. abietina var. abietina was introduced into North America early in the century, most likely on asymptomatic infected pine seedlings, and is currently widespread in eastern North America. In order to detect latent infections and differentiate the North American and European races of the fungus, we developed oligonucleotide primers to amplify by PCR portions of the ITS of the ribosomal DNA of G. abietina var. abietina. The 417 bp amplified DNA fragment comprises two Msp I restriction sites in the NA race but only one in the EU race. DNA extractions directly from infected asymptomatic needles, or from single fruiting bodies, followed by PCR amplification and Msp I digestion allowed the detection and race identification of both races of G. abietina var. abietina from seedlings and branches of Pinus resinosa and P. banksiana. A nested PCR assay was sensitive enough to detect the equivalent of a single infected seedling in a bulk sample of 1000 healthy seedlings. Validation tests were conducted by comparing PCR and isolation assays with 104 fascicles. All samples for which the fungus was isolated yielded a positive PCR assay and there was no false negative, i.e. samples for which the fungus was isolated but not detected by PCR. Among the samples from which the fungus was not isolated, most yielded a negative PCR assay (71%), but a proportion (29%) yielded positive PCR assays. In several of those cases, aggressive contaminants had apparently overgrown the pathogen. The method described here can lead to the detection and race identification of the NA and EU races of G. abietina var. abietina directly from infected tissues without the need to culture the fungus and should find applications in nursery inspection and quarantine.