Maximum daily energy intake: It takes time to lift the metabolic ceiling

Conventionally, maximum capacities for energy assimilation are presented as daily averages. However, maximum daily energy intake is determined by the maximum metabolizable energy intake rate and the time available for assimilation of food energy Thrush nightingales (Luscinia luscinia) in migratory disposition were given limited food rations for 3 d to reduce their energy stores. Subsequently, groups of birds were fed ad lib. during fixed time periods varying between 7 and 23 h per day. Metabolizable energy intake rate, averaged over the available feeding time, was 1.9 W and showed no difference between groups on the first day of refueling. Total daily metabolizable energy intake increased linearly with available feeding time, and for the 23-h group, it was well above suggested maximum levels for animals. We conclude that both intake rate and available feeding time must be taken into account when interpreting potential constraints acting on animals' energy budgets. In the 7-h group, energy intake rates increased from 1.9 W on the first day to 3.1 W on the seventh day. This supports the idea that small birds can adaptively increase their energy intake rates on a short timescale

A multi-scale model for diffusion of large molecules in steam-exploded wood

In this paper, multi-scale modeling was used to resolve diffusion in steam-exploded wood at tracheid scales including sub-micrometer features of bordered pits. Simulations were performed using the lattice Boltzmann method with high-resolution X-ray tomography image data as the input for the microstructure. The results show an effective method for utilizing a variable diffusion coefficient to implement two length scales. This circumvents the need to resolve the bordered pits in detail, which requires massive computing power. Instead, the effective diffusion coefficient for one bordered pit is used as input for this model. Results based on the present model are comparable to experimental data. This methodology can be extended to more structural features at the microscale of wood, such as latewood and the cell wall. Obtaining a map of different diffusion coefficients based on features and scale gives a better overall understanding of diffusion and the importance of mass transport with regard to the pretreatment of wood

Lattice Boltzmann simulations of diffusion in steam-exploded wood

Diffusion of large molecules throughout the porous microstructure of wood pretreated with steam explosion was investigated by using the lattice Boltzmann method for simulations. Wood samples were investigated with high-resolution X-ray tomography to effectively reconstruct an accurate geometry of the structural changes that ensue after pretreatment. Samples of approximately 1\ua0mm3 with voxel sizes from 0.5 to 1\ua0μm were examined with X-ray imaging. These large volumes, relative to what reasonably can be simulated, were divided into sub-volumes and were further reconstructed into geometries suited for the LBM simulations. The transient development of the concentration was investigated, and the effective diffusion coefficient at steady state was computed. Diffusion rates were found to increase significantly in the transversal direction due to the steam explosion pretreatment. The increase was observed both in the time needed for solutes to diffuse throughout the pores and in the effective diffusion coefficient. A shorter diffusion pathway and a higher connectivity between pores were found for the pretreated samples, even though the porosity was similar and the pore size distribution narrower than the native sample. These results show that local mass transport depends not only on porosity but also, in a complex manner, on pore structure. Thus, a more detailed analysis of pore space structure using tomography data, in combination with simulations, enables a more general understanding of the diffusional process

Non-coding antisense transcription detected by conventional and single-stranded cDNA microarray

<p>Abstract</p> <p>Background</p> <p>Recent studies revealed that many mammalian protein-coding genes also transcribe their complementary strands. This phenomenon raises questions regarding the validity of data obtained from double-stranded cDNA microarrays since hybridization to both strands may occur. Here, we wanted to analyze experimentally the incidence of antisense transcription in human cells and to estimate their influence on protein coding expression patterns obtained by double-stranded microarrays. Therefore, we profiled transcription of sense and antisense independently by using strand-specific cDNA microarrays.</p> <p>Results</p> <p>Up to 88% of expressed protein coding loci displayed concurrent expression from the complementary strand. Antisense transcription is cell specific and showed a strong tendency to be positively correlated to the expression of the sense counterparts. Even if their expression is wide-spread, detected antisense signals seem to have a limited distorting effect on sense profiles obtained with double-stranded probes.</p> <p>Conclusion</p> <p>Antisense transcription in humans can be far more common than previously estimated. However, it has limited influence on expression profiles obtained with conventional cDNA probes. This can be explained by a biological phenomena and a bias of the technique: a) a co-ordinate sense and antisense expression variation and b) a bias for sense-hybridization to occur with more efficiency, presumably due to variable exonic overlap between antisense transcripts.</p