Nothing Lasts Forever: Environmental Discourses on the Collapse of Past Societies

The study of the collapse of past societies raises many questions for the theory and practice of archaeology. Interest in collapse extends as well into the natural sciences and environmental and sustainability policy. Despite a range of approaches to collapse, the predominant paradigm is environmental collapse, which I argue obscures recognition of the dynamic role of social processes that lie at the heart of human communities. These environmental discourses, together with confusion over terminology and the concepts of collapse, have created widespread aporia about collapse and resulted in the creation of mixed messages about complex historical and social processes

Viscous and elastic properties of water-soluble cellulosic derivatives regarding to application

Cellulose derivatives as an example for water soluble polymers from renewable resources have gained great importance for the industrial application over the last years. However, the flow property profile of aqueous solutions of cellulose derivatives is not only depending on the chemical composition and substitution pattern, solvent, temperature and concentration but also on the molar mass and the particle size in solution. A correlation of these structure properties with the shear flow properties like the viscosity yield of a cellulose derivative can be obtained for each homologous derivative series of a specific degree of substitution via empirical relationships as the Mark-Houwink-Sakurada-relationship ([]-M- relationship), the 0-[]-c relationship or the -[]-c and the N1-[]-c relationship for the elastic properties of a solution. The elastic response can also be captured via oscillatory agitation of a sample that yields the moduli and hence the network parameters of the cellulose derivative in solution. However, to fully characterize the flow properties in technically relevant problems, also the elongational properties of a solution need to be determined. Lately it could be shown that this is now possible for aqueous solutions of cellulose derivatives with capillary break-up extensional rheometry (CaBER) experiments [1], which probe the transient behaviour of fluid threads of polymer solutions to extract the transient extensional viscosity and relaxation times to correlate these material functions with others of the rheological cycle and the molar mass and the molar mass distribution (MWD).status: publishe

How dilute are dilute solutions in extensional flows?

We investigate the concentration dependence of the characteristic relaxation time of dilute polymer solutions in transient uniaxial elongational flow. A series of monodisperse polystyrene solutions of five different molecular weights (1.8 X 10(6) <= M <= 8.3 X 10(6) g/mol) with concentrations spanning five orders of magnitude were dissolved in two solvents of differing solvent quality (diethylphthalate and oligomeric styrene). Optical measurements with a capillary breakup extensional rheometer of the rate of filament thinning and the time to breakup in each fluid are used to determine the characteristic relaxation time. A criterion for a lower sensitivity limit is introduced, in the form of a minimum concentration C in necessary for experimental resolution of the effects of polymeric viscoelasticity. This criterion is validated by experiment and comparison to numerical calculations with a multimode bead-spring dumbbell model. These calculations also rationalize previous paradoxical observations of extensional thinning in fluid threads of ultradilute polymer solutions in which stress relaxation apparently occurred faster than predicted by the Zimm theory. Above this minimum sensitivity limit we show that the effective relaxation time of moderately dilute solutions (0.01 <= c/c*<= 1) in transient extensional flow rises substantially above the fitted value of the relaxation time extracted from small amplitude oscillatory shear flow and above the Zimm relaxation time computed from kinetic theory and intrinsic viscosity measurements. This effective relaxation time exhibits a power-law scaling with the reduced concentration (c/c*) and the magnitude of the exponent varies with the thermodynamic quality of the solvent. The scaling of this "self-concentration" effect appears to be roughly consistent to that predicted when the dynamics of the partially elongated and overlapping polymer chains are described within the framework of blob theories for semi-dilute solutions. (c) 2006 The Society of Rheology.status: publishe

Environmental Sensibility and Human Values as Factors for Forming European Ecotourist Market Segments

This study examines the relationship between environmental attitudes and human value sets in forming an eco-tourist market segment within the European region. Different studies indicated that environmental attitudes reflected in general motivations were closely and positively related. Some findings showed that the examination of environmental attitudes that concern psychological factors (motivation) could be more powerful and meaningful than socio-demographic characteristics. The purpose of this study is to examine if human values that indicate basic motivational aspects, when inter-related with high environmental sensibility shared by different people from Europe, could be used for the creation of a specific market segmentation model. The findings identified three main factors that determine tourist values, while at the same time, the multiple discriminant analysis indicated the existence of several clusters, allowing for an identification of ‘eco-friendly’ tourist segments. By using data collections from the European Social Survey, the model also allowed comparability between surveyed countries by crosschecking multiple psycho-sociological and demographic factors, focusing on the environmentally sensitive groups, the so-called ‘eco-careful’ (hard) and ‘eco-sensible’ (soft) tourists. Furthermore, the study looked at potential demand markets that are interested in preserved nature, recreation, and adventure tours. The study confirmed that basic human values play an important role in explaining motivation aspects in tourism-related choices

Effects of sleep and wake on astrocytes: clues from molecular and ultrastructural studies

BACKGROUND: Astrocytes can mediate neurovascular coupling, modulate neuronal excitability, and promote synaptic maturation and remodeling. All these functions are likely to be modulated by the sleep/wake cycle, because brain metabolism, neuronal activity and synaptic turnover change as a function of behavioral state. Yet, little is known about the effects of sleep and wake on astrocytes. RESULTS: Here we show that sleep and wake strongly affect both astrocytic gene expression and ultrastructure in the mouse brain. Using translating ribosome affinity purification technology and microarrays, we find that 1.4 % of all astrocytic transcripts in the forebrain are dependent on state (three groups, sleep, wake, short sleep deprivation; six mice per group). Sleep upregulates a few select genes, like Cirp and Uba1, whereas wake upregulates many genes related to metabolism, the extracellular matrix and cytoskeleton, including Trio, Synj2 and Gem, which are involved in the elongation of peripheral astrocytic processes. Using serial block face scanning electron microscopy (three groups, sleep, short sleep deprivation, chronic sleep restriction; three mice per group, >100 spines per mouse, 3D), we find that a few hours of wake are sufficient to bring astrocytic processes closer to the synaptic cleft, while chronic sleep restriction also extends the overall astrocytic coverage of the synapse, including at the axon–spine interface, and increases the available astrocytic surface in the neuropil. CONCLUSIONS: Wake-related changes likely reflect an increased need for glutamate clearance, and are consistent with an overall increase in synaptic strength when sleep is prevented. The reduced astrocytic coverage during sleep, instead, may favor glutamate spillover, thus promoting neuronal synchronization during non-rapid eye movement sleep. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12915-015-0176-7) contains supplementary material, which is available to authorized users