Tidal propagation in strongly convergent channels

Simple first‐ and second‐order analytic solutions, which diverge markedly from classical views of cooscillating tides, are derived for tidal propagation in strongly convergent channels. Theoretical predictions compare well with observations from typical examples of shallow, “funnel‐shaped” tidal estuaries. A scaling of the governing equations appropriate to these channels indicates that at first order, gradients in cross‐sectional area dominate velocity gradients in the continuity equation and the friction term dominates acceleration in the momentum equation. Finite amplitude effects, velocity gradients due to wave propagation, and local acceleration enter the equations at second order. Applying this scaling, the first‐order governing equation becomes a first‐order wave equation, which is inconsistent with the presence of a reflected wave. The solution is of constant amplitude and has a phase speed near the frictionless wave speed, like a classical progressive wave, yet velocity leads elevation by 90°, like a classical standing wave. The second‐order solution at the dominant frequency is also a unidirectional wave; however, its amplitude is exponentially modulated. If inertia is finite and convergence is strong, amplitude increases along channel, whereas if inertia is weak and convergence is limited, amplitude decays. Compact solutions for second‐order tidal harmonics quantify the partially canceling effects of (1) time variations in channel depth, which slow the propagation of low water, and (2) time variations in channel width, which slow the propagation of high water. Finally, it is suggested that phase speed, along‐channel amplitude growth, and tidal harmonics in strongly convergent channels are all linked by morphodynamic feedback

On the abundance of non-cometary HCN on Jupiter

Using one-dimensional thermochemical/photochemical kinetics and transport models, we examine the chemistry of nitrogen-bearing species in the Jovian troposphere in an attempt to explain the low observational upper limit for HCN. We track the dominant mechanisms for interconversion of N2-NH3 and HCN-NH3 in the deep, hightemperature troposphere and predict the rate-limiting step for the quenching of HCN at cooler tropospheric altitudes. Consistent with other investigations that were based solely on time-scale arguments, our models suggest that transport-induced quenching of thermochemically derived HCN leads to very small predicted mole fractions of hydrogen cyanide in Jupiter's upper troposphere. By the same token, photochemical production of HCN is ineffective in Jupiter's troposphere: CH4-NH3 coupling is inhibited by the physical separation of the CH4 photolysis region in the upper stratosphere from the NH3 photolysis and condensation region in the troposphere, and C2H2-NH3 coupling is inhibited by the low tropospheric abundance of C2H2. The upper limits from infrared and submillimeter observations can be used to place constraints on the production of HCN and other species from lightning and thundershock sources.Comment: 56 pages, 0 tables, 6 figures. Submitted to Faraday Discussions [in press

The travel behaviour intentions of young people in the context of climate change

This article examines the factors influencing the future travel behaviour intentions of young people (aged 11-18), with specific attention given to how climate change considerations affect these. Overall it is found that the participants' travel behaviour intentions are dominated by a desire to drive and that their values relating to identity, self-image, and social recognition (at the expense of their environmental values), as well as their affective attitudes towards transport modes, are key influences on this. Although they are aware of climate change, the participants' understanding of the link between transport and climate change was weak. At the same time, they illustrated an apathy towards climate change - in part due to the timing and intangibility of its associated impacts and their lack of self-efficacy with respect to tackling this issue. However, despite claiming that their current environmentally friendly travel behaviours (such as walking or cycling to school) are not influenced by the issue of climate change, a number are accepting of the idea of enforced travel behaviour change - away from use of the car, towards more 'environmentally friendly' modes. This acceptance was in part due to their belief that such action would remove the influence of the 'social dilemma', where their own efforts to tackle climate change may be rendered worthless by the inaction of others. © 2009 Elsevier Ltd. All rights reserved

Are Counterpossibles Epistemic?

It has been suggested that intuitions supporting the nonvacuity of counterpossibles can be explained by distinguishing an epistemic and a metaphysical reading of counterfactuals. Such an explanation must answer why we tend to neglect the distinction of the two readings. By way of an answer, I offer a generalized pattern for explaining nonvacuity intuitions by a stand-and-fall relationship to certain indicative conditionals. Then, I present reasons for doubting the proposal: nonvacuists can use the epistemic reading to turn the table against vacuists, telling apart significant from spurious intuitions. Moreover, our intuitions tend to survive even if we clear-headedly intend a metaphysical reading

Annotation of the Drosophila melanogaster euchromatic genome: a systematic review

BACKGROUND: The recent completion of the Drosophila melanogaster genomic sequence to high quality and the availability of a greatly expanded set of Drosophila cDNA sequences, aligning to 78% of the predicted euchromatic genes, afforded FlyBase the opportunity to significantly improve genomic annotations. We made the annotation process more rigorous by inspecting each gene visually, utilizing a comprehensive set of curation rules, requiring traceable evidence for each gene model, and comparing each predicted peptide to SWISS-PROT and TrEMBL sequences. RESULTS: Although the number of predicted protein-coding genes in Drosophila remains essentially unchanged, the revised annotation significantly improves gene models, resulting in structural changes to 85% of the transcripts and 45% of the predicted proteins. We annotated transposable elements and non-protein-coding RNAs as new features, and extended the annotation of untranslated (UTR) sequences and alternative transcripts to include more than 70% and 20% of genes, respectively. Finally, cDNA sequence provided evidence for dicistronic transcripts, neighboring genes with overlapping UTRs on the same DNA sequence strand, alternatively spliced genes that encode distinct, non-overlapping peptides, and numerous nested genes. CONCLUSIONS: Identification of so many unusual gene models not only suggests that some mechanisms for gene regulation are more prevalent than previously believed, but also underscores the complex challenges of eukaryotic gene prediction. At present, experimental data and human curation remain essential to generate high-quality genome annotations