Abstract A review of geochronological data underlying the geological timescale for the Triassic yields a significantly different timescale calibration than that published in the most recent compilation (Geologic TimeScale 2004). This is partly due to the availability of new radio–isotopic data, but mostly because strict selection criteria are applied and complications arising from biases (both systematic and random) are accounted for in this contribution. The ages for the base and the top of the Triassic are constrained by U–Pb ages to 252.3 and 201.5 Ma, respectively. These dates also constrain the ages of major extinction events at the Permian–Triassic and Triassic–Jurassic boundaries, and are statistically indistinguishable from ages obtained for the Siberian Traps and volcanic products from the Central Atlantic Magmatic Province, respectively, suggesting a causal link. Ages for these continental volcanics, however, are mostly from the K–Ar ( 40 Ar/ 39 Ar) system, which requires accounting and correcting for a systematic bias of c . 1% between U–Pb and 40 Ar/ 39 Ar isotopic ages (the 40 Ar/ 39 Ar ages being younger). Robust age constraints also exist for the Induan–Olenekian boundary (251.2 Ma) and the Early–Middle Triassic (Olenekian–Anisian) boundary (247.2 Ma), resulting in a surprisingly short duration of the Early Triassic, which has implications for the timing of biotic recovery and major changes in ocean chemistry during this time. Furthermore, the Anisian–Ladinian boundary is constrained to 242.0 Ma by new U–Pb and 40 Ar/ 39 Ar ages. Radio–isotopic ages for the Late Triassic are scarce, and the only reliable and biostratigraphically-controlled age is from an upper Carnian tuff dated to 230.9 Ma, yielding a duration of more than 35 Ma for the Late Triassic. All of these ages are from U–Pb analyses applied to zircons with uncertainties at the permil level or better. The resulting compilation can only serve as a guideline and must be considered a snapshot, resolving some of the issues mainly associated with inaccurate and misinterpreted data in previous publications. However, further advances will require revision of some of the data presented here.
Plasmids have cell cycle replication patterns that need to be considered in models of their replication dynamics. To compare current theories for control of plasmid replication with experimental data for timing of plasmid replication with the cell cycle, a Monte Carlo simulation of plasmid replication and partition was developed. High-copy plasmid replication was simulated by incorporating equations previously developed from the known molecular biology of ColE1-type plasmids into the cell-cycle simulation. Two types of molecular mechanisms for low-copy plasmid replication were tested: accumulation of an initiator protein in proportion to cell mass and binding of the plasmid origin to the cell membrane. The low-copy plasmids were partitioned actively, with a specific mechanism to mediate the transfer from mother to daughter cells, whereas the high-copy plasmids were partitioned passively with cell mass.The simulation results and experimental data demonstrate cell-cycle-specific replication for the low-copy F plasmid and cell-cycle-independent replication for the high-copy pBR322, ColBM, and R6K plasmids. The simulation results indicate that synchronous replication at multiple plasmid origins is critical for the cell-cycle-specific pattern observed in rapidly growing cells. Variability in the synchrony of initiation of multiple plasmid origins give rise to a cell-cycle-independent pattern and is offered as a plausible explanation for the controversy surrounding the replication pattern of the low-copy plasmids. A comparison of experimental data and simulation results for the low-copy F plasmid at several growth rates indicates that either initiation mechanism would be sufficient to explain the timing of replication with the cell cycle. The simulation results also demonstrate that, although cell-cycle-specific and cell-cycle independent replication patterns give rise to very different gene-expression patterns during short induction periods in age-selected populations, long-term expression of genes encoded on low-copy and high-copy plasmids in exponentially growing cells have nearly the same patterns. These results may be important for the future use of low-copy plasmids as expression vectors and validate the use of simpler models for high-copy plasmids that do not consider cell-cycle phenomena. (c) 1996 John Wiley & Sons, Inc.
The positive association between the service sector share of output and per capita income is one of the best-known regularities in all of growth and development economics. Yet there is less than complete agreement on the nature of that association. Here we identify two waves of service sector growth, a first wave in countries with relatively low levels of per capita GDP and a second wave in countries with higher per capita incomes. The first wave appears to be made up primarily of traditional services, the second wave of modern (financial, communication, computer, technical, legal, advertising and business) services that are receptive to the application of information technologies and increasingly tradable across borders. In addition, there is evidence of the second wave occurring at lower income levels after 1990. But this change in the second wave is not equally evident in all economies: it is most apparent in democracies, in countries that are open to trade, and in those that are relatively close to the major global financial centers. This points to both political and economic conditions that can help countries capitalize on the opportunities afforded by an increasingly globalized post-industrial economy.
This paper discusses a new approach to dynamic simulation called impulse-based simulation. We have focused on the twin goals of physical accuracy and computational efficiency. Our simulator can accurately model complex dynamic systems in real time. The organization of this paper is as follows. Section 2 gives an overview of the impulse-based method for dynamic simulation, highlighting its differences from and advantages over more traditional constraint-based methods. Section 3 describes collision check scheduling, and how this standard bottleneck in dynamic simulation can be streamlined. Section 4 discusses our method of resolving collisions between bodies. We treat collisions in a fully general manner, accounting for friction as well as non-perfectly elastic behavior. Correctly computing collision impulses is critical for achieving physically accurate simulations. Finally, section 5 describes some of the simulations wehave performed with our simulator, illustrating the speed and accuracy of the approach, and mentions some future work
Staatsräson ist ein schillernder Begriff, der sowohl positive wie negative Elemente enthält. Jeder Staat hat einen harten Kern von Werten, Zielen und Gewissheiten, die man als Staatsräson im positiven Sinne bezeichnen könnte. Die dunkle Seite der Staatsräson, die rücksichtslose Durchsetzung von Staatszielen mit Gewalt, schien hingegen im liberalen demokratischen Rechtsstaat der Gegenwart überwunden zu sein. Der weltweite Kampf gegen den Terrorismus lässt das Pendel jedoch wieder in die andere Richtung ausschlagen.
