The effect of the solar field reversal on the modulation of galactic cosmic rays

There is now a growing awareness that solar cycle related changes in the large-scale structure of the interplanetary magnetic field (IMF) may play an important role in the modulation of galactic cosmic rays. To date, attention focussed on two aspects of the magnetic field structure: large scale compression regions produced by fast solar wind streams and solar flares, both of which are known to vary in intensity and number over the solar cycle, and the variable warp of the heliospheric current sheet. It is suggested that another feature of the solar cycle is worthy of consideration: the field reversal itself. If the Sun reverses its polarity by simply overturning the heliospheric current sheet (northern fields migrating southward and vice-versa) then there may well be an effect on cosmic ray intensity. However, such a simple picture of solar reversal seems improbable. Observations of the solar corona suggest the existence of not one but several current sheets in the heliosphere at solar maximum. The results of a simple calculation to demonstrate that the variation in cosmic ray intensities that will result can be as large as is actually observed over the solar cycle are given

How slowing senescence changes life expectancy

Mortality decline has historically been a result of reductions in the level of mortality at all ages. The slope of mortality increase with age has been remarkably stable. A number of leading researchers on aging, however, suggest that the next revolution of longevity increase will be the result of slowing down the rate of aging, lessening the rate at which mortality increases as we get older. In this paper, we show mathematically how varying the pace of senescence influences life expectancy. We provide a formula that holds for any baseline hazard function. Our result is analogous to Keyfitz's "entropy" relationship for changing the level of mortality. Interestingly, the influence of the shape of the baseline schedule on the effect of senescence changes is the complement of that found for level changes. We also provide a generalized formulation that mixes level and slope effects.

Cohort postponement and period measures

We introduce a new class of models in which demographic behavior such as fertility is postponed by differing amounts depending only on cohort membership. We show how this model fits into a general framework of period and cohort postponement that includes the existing models in the literature, notably those of Bongaarts and Feeney and Kohler and Philipov. The cohort-based model shows the effects of cohort shifts on period fertility measures and provides an accompanying tempo-adjusted measure of period total fertility in the absence of observed shifts. Simulation reveals that when postponement is governed by cohorts, the cohort-based indicator outperforms the Bongaarts and Feeney model that is now in widespread use. The cohort-based model is applied to fertility in several modern populations.

Glasnost in the GDR?: the East German Writers Congress of 1987

By the late 1980s many East German authors had for years called for expanding what could be said publicly about the ruling regime. The ruling Socialist Unity Party (SED) was quick to suppress such rhetoric, however, and many fellow writers condemned outspoken colleagues for providing ammunition to the West. Yet after years of struggle, the year 1987 witnessed an eruption of public criticism during the Tenth Writers Congress, hosted by the East German Writers Union, the governmentdominated organization to which all authors had to belong. These congresses were typically propaganda events, but in 1987, inspired by Mikhail Gorbachev's calls for greater openness in the USSR, several authors, in front of the media, interrogated many aspects of the dictatorship, stunning the SED elite and secret police in the process. This article explores the congress, tracing the Writers Union's role in shaping debates about freedom of expression. Changes in the preceding years meant that by 1987, critical views had become more widespread, including among those who had once condemned nonconformists. Consequently, at the congress a critical mass of writers succeeded in expanding the limits of speech, joining a wider call for liberalization across the communist world

Propagation of a Topological Transition: the Rayleigh Instability

The Rayleigh capillary instability of a cylindrical interface between two immiscible fluids is one of the most fundamental in fluid dynamics. As Plateau observed from energetic considerations and Rayleigh clarified through hydrodynamics, such an interface is linearly unstable to fission due to surface tension. In traditional descriptions of this instability it occurs everywhere along the cylinder at once, triggered by infinitesimal perturbations. Here we explore in detail a recently conjectured alternate scenario for this instability: front propagation. Using boundary integral techniques for Stokes flow, we provide numerical evidence that the viscous Rayleigh instability can indeed spread behind a front moving at constant velocity, in some cases leading to a periodic sequence of pinching events. These basic results are in quantitative agreement with the marginal stability criterion, yet there are important qualitative differences associated with the discontinuous nature of droplet fission. A number of experiments immediately suggest themselves in light of these results.Comment: 15 pages, 7 figures, Te

The Technological and Socio-Economic Organization of the Elmenteitan Early Herders in Southern Kenya (3000-1200 BP)

Understanding how the modern world has been shaped by the origins and spread of food production deeper in our past is an enduring and fundamental goal of anthropological archaeology. In Africa, mobile pastoralism emerged as a way of life that is economically and ideologically focused on herding livestock, and spread across the continent over the last 8000 years. Despite the potential importance of African pastoralism within global dialogues on the origins of food production, the social and economic systems that sustained its spread through the continent remain poorly understood. A culture-complex known as the Elmenteitan is associated with the spread of stone-tool using herders into southern Kenya, and the development of a long-distance obsidian exchange system stemming from a single quarry site on top of Mt. Eburru from 3000-1400 years ago. This dissertation uses the Elmenteitan case-study to mount the first comprehensive study of how economic needs, environmental conditions, and socio-cultural institutions shaped ancient pastoralist technological strategies. To accomplish this I directed archaeological surveys and excavations at the Elmenteitan Obsidian Quarry on Mt. Eburru to test hypotheses regarding the social systems involved in herder obsidian procurement. I engaged in intensive analysis of stone tool debris at the quarry in order to establish a start point for a larger comparative analysis of 12 lithic assemblages from Elmenteitan sites spread across southwestern Kenya. Based on archaeological and lithic datasets, I demonstrate that Elmenteitan herders deployed a regionally uniform lithic technology that emphasized flexibility in responding to environmental diversity and climatic change. I show that this form of technological organization was supported by a system of obsidian access and distribution that was maintained through investment in social institutions that bound Elmenteitan communities into a system of reciprocity, alliance, and cultural identity. I conclude that the integration of social, economic, and technological systems developed as strategy for ensuring long-term risk mitigation in unpredictable environments