Viscous energy dissipation in slender channels with porous or semipermeable walls.

We study the viscous dissipation in pipe flows in long channels with porous or semipermeable walls, taking into account both the dissipation in the bulk of the channel and in the pores. We give simple closed-form expressions for the dissipation in terms of the axially varying flow rate Q(x) and the pressure p(x), generalizing the well-known expression W[over ̇]=QΔp=RQ^{2} for the case of impenetrable walls with constant Q, pressure difference Δp between the ends of the pipe and resistance R. When the pressure p_{0} outside the pipe is constant, the result is the straightforward generalization W[over ̇]=Δ[(p-p_{0})Q].

Direct Comparison of Leaf Plasmodesma Structure and Function in Relation to Phloem-Loading Type.

The export of photosynthetically produced sugars from leaves depends on plasmodesmatal transport of sugar molecules from mesophyll to phloem. Traditionally, the density of plasmodesmata (PD) along this phloem-loading pathway has been used as a defining feature of different phloem-loading types, with species proposed to have either many or few PD between the phloem and surrounding cells of the leaf. However, quantitative determination of PD density has rarely been performed.

Sugar export limits size of conifer needles.

Plant leaf size varies by more than three orders of magnitude, from a few millimeters to over one meter. Conifer leaves, however, are relatively short and the majority of needles are no longer than 6 cm. The reason for the strong confinement of the trait-space is unknown.

Diffusion and bulk flow in phloem loading: a theoretical analysis of the polymer trap mechanism for sugar transport in plants.

Plants create sugar in the mesophyll cells of their leaves by photosynthesis. This sugar, mostly sucrose, has to be loaded via the bundle sheath into the phloem vascular system (the sieve elements), where it is distributed to growing parts of the plant. We analyze the feasibility of a particular loading mechanism, active symplasmic loading, also called the polymer trap mechanism, where sucrose is transformed into heavier sugars, such as raffinose and stachyose, in the intermediary-type companion cells bordering the sieve elements in the minor veins of the phloem.

Immobilisation and characterisation of the demineralised, fully hydrated organic matrix of nacre--an atomic force microscopy study.

Mimicry of the tough natural composite nacre in future bioengineering requires knowledge of the biomineralisation process. The insoluble organic matrix isolated from the shell of the gastropod Haliotis laevigata was characterised by protein chemistry, topographical and mechanical measurements. Demineralisation of nacre in dilute acetic acid or ethylenediaminetetraacetic acid revealed a set of soluble proteins and the insoluble matrix.

Detection of interaction between biomineralising proteins and calcium carbonate microcrystals.

The natural composite nacre is characterised by astonishing mechanical properties, although the main constituent is a brittle mineral shaped as tablets interdispersed by organic layers. To mimic the natural formation process which takes place at ambient conditions an understanding of the mechanism responsible for a defined microstructure of nacre is necessary. Since proteins are assumed to be involved in this mechanism, it is advantageous to identify distinct proteins interacting with minerals from the totality of proteins contained in nacre.