Palaeobiology: Argentinian unhatched pterosaur fossil

Our knowledge of the eggs and embryos of pterosaurs, the Mesozoic flying reptiles, is sparse. Until now, the recent discovery of an ornithocheirid embryo from 121-million-year-old rocks in China constituted the only reliable evidence of an unhatched pterosaur. Here we describe an embryonic fossil of a different pterosaur from the Early Cretaceous lacustrine deposits of Loma del Pterodaustro (the Lagarcito Formation, which is about 100 million years old) in central Argentina. This new fossil provides insight into the eggshell morphology, early growth and nesting environments of pterosaurs.     

Variable female preferences drive complex male displays

Complexity in male sexual displays is widely appreciated but diversity in female mate choice has received little attention. Males of many species have sexual displays composed of multiple display traits, and females are thought to use these different traits in mate choice. Models of multiple display trait evolution suggest that these traits provide females with different kinds of information in different stages of the mate choice process, or function as redundant signals to improve the accuracy of mate assessment. We suggest that complex male displays might also arise because of variation in female preferences for particular male display traits. The causes of female preference variation have received little attention, and the role of preference variation in shaping complex male displays is unclear. Here we show that in satin bowerbirds (Ptilonorhynchus violaceus) female mate choice is a multistage process, where females of different ages use different male display traits in successive stages. Age- and stage-specific female preferences may contribute to explaining the widespread occurrence of multifaceted male displays.     

A 1.7-kilobase single-stranded DNA that folds into a nanoscale octahedron

Molecular self-assembly offers a means of spontaneously forming complex and well-defined structures from simple components. The specific bonding between DNA base pairs has been used in this way to create DNA-based nanostructures and to direct the assembly of material on the subnanometre to micrometre scale. In principle, large-scale clonal production of suitable DNA sequences and the directed evolution of sequence lineages towards optimized behaviour can be realized through exponential DNA amplification by polymerases. But known examples of three-dimensional geometric DNA objects are not amenable to cloning because they contain topologies that prevent copying by polymerases. Here we report the design and synthesis of a 1,669-nucleotide, single-stranded DNA molecule that is readily amplified by polymerases and that, in the presence of five 40-mer synthetic oligodeoxynucleotides, folds into an octahedron structure by a simple denaturation-renaturation procedure. We use cryo-electron microscopy to show that the DNA strands fold successfully, with 12 struts or edges joined at six four-way junctions to form hollow octahedra approximately 22 nanometres in diameter. Because the base-pair sequence of individual struts is not repeated in a given octahedron, each strut is uniquely addressable by the appropriate sequence-specific DNA binder.     

Calorie restriction extends Saccharomyces cerevisiae lifespan by increasing respiration

Calorie restriction (CR) extends lifespan in a wide spectrum of organisms and is the only regimen known to lengthen the lifespan of mammals. We established a model of CR in budding yeast Saccharomyces cerevisiae. In this system, lifespan can be extended by limiting glucose or by reducing the activity of the glucose-sensing cyclic-AMP-dependent kinase (PKA). Lifespan extension in a mutant with reduced PKA activity requires Sir2 and NAD (nicotinamide adenine dinucleotide). In this study we explore how CR activates Sir2 to extend lifespan. Here we show that the shunting of carbon metabolism toward the mitochondrial tricarboxylic acid cycle and the concomitant increase in respiration play a central part in this process. We discuss how this metabolic strategy may apply to CR in animals.     

Dealing with coercion: Critical Systems Heuristics and beyond

This paper begins with an introduction to the philosophy and methodology of Critical Systems Heuristics (CSH). Following this, various citicisms of CSH are reviewed. One particularly important criticism is that CSH should not be seen as a replacement for other systems approaches, but as complementary to them. It is this idea of complementarity that has led several Critical Systems thinkers to take CSH, along with a number of other systems methods, and try to show that they are most appropriately used in different contexts. CSH, it is said, is at its most useful when we are confronted with coercive situations. However, in this paper it is argued that coercion is usually characterised by closure of debate. Therefore CSH, which depends upon the possibility of communication (or arbitration) between stakeholder groups, becomes redundant when coercion is experienced. It is further argued that coercion can only be addressed adequately by widening our definition of systems practice to include campaigning and direct political action. There is still considerable scope for developing these areas in the systems domain.     

面向表单的分析：一种基于表单的应用程序模型的新方法

在软件工程中，企业系统最为吸引人也是最为需求的。本书对企业系统建模作概念性的介绍和全面地综述。提出了分析与设计基于表单的企业系统的一种特殊目的建模技术。对特殊领域建模语言一直存在着强烈的需求。本书的作者来自科学家和对此类商业应用程序有兴趣的专业人员，他们以一种创新的方法修改了已被广泛接受的基本建模技术，实现对所需应用程序领域建模框架的优化。     

Developing the methodology of TSI: From the oblique use of methods to creative design

During the last 13 years, a dialogue has been conducted in the Critical Systems literature on the subject of choice betwen methods. However, in the late 1980s and early 1990s, researchers went in two separate directions. One direction involved an exploration of the “creative design of methods.” This is when the problem situation is understood in terms of a series of systemically interrelated research questions, each of which might need to be addressed using a different method, or part of a method. A synthesis is generated that allows each individual research question to be addressed as part of a whole system of questions. The other research direction involved the development of “Total Systems Intervention” (TSI), a meta-methodology that, amongst other things, encourages the creative exploration of the problem situation prior to the choice of methods. One of the latest innovations in TSI is a theory of the “oblique” use of methods. This is the use of methods for purposes other than those they were originally designed for. However, it is argued here that all the case studies that have been subject to an “oblique” interpretation can be better explained if they are seen as examples of the creative design of methods. We can therefore bring together the two strands of research that have hitherto been pursued separately in the Critical Systems literature. it is suggested that TSI can be enhanced by an understanding of the creative design of methods because the latter allows us to explain the purposive, flexible, and responsive way in which TSI is most successfully used in practice.     

Antagonism of amphetamine stereotyped behavior by diastereoisomeric dihydrodibenzothiepin neuroleptics

Summary Differences in neuroleptic activity were observed between the diastereoisomers of a dihydrodibenzothiepin derivative, while no potency differences were seen between their respective enantiomorphs.Supported by USPHS grant NS-10203.