A mathematical model of plant nutrient uptake

The classical model of plant root nutrient uptake due to Nye. Tinker and Barber is developed and extended. We provide an explicit closed formula for the uptake by a single cylindrical root for all cases of practical interest by solving the absorption-diffusion equation for the soil nutrient concentration asymptotically in the limit of large time. We then use this single root model as a building block to construct a model which allows for root size distribution in a more realistic plant root system, and we include the effects of root branching and growth. The results are compared with previous theoretical and experimental studies

Mathematical models of avascular cancer

This review will outline a number of illustrative mathematical models describing the growth of avascular tumours. The aim of the review is to provide a relatively comprehensive list of existing models in this area and discuss several representative models in greater detail. In the latter part of the review, some possible future avenues of mathematical modelling of avascular tumour development are outlined together with a list of key questions

Mathematical models of avascular cancer

This review will outline a number of illustrative mathematical models describing the growth of avascular tumours. The aim of the review is to provide a relatively comprehensive list of existing models in this area and discuss several representative models in greater detail. In the latter part of the review, some possible future avenues of mathematical modelling of avascular tumour development are outlined together with a list of key questions

Unraveling Heterogeneity in Epithelial Cell Fates of the Mammary Gland and Breast Cancer.

Fluidity in cell fate or heterogeneity in cell identity is an interesting cell biological phenomenon, which at the same time poses a significant obstacle for cancer therapy. The mammary gland seems a relatively straightforward organ with stromal cells and basal- and luminal- epithelial cell types. In reality, the epithelial cell fates are much more complex and heterogeneous, which is the topic of this review. Part of the complexity comes from the dynamic nature of this organ: the primitive epithelial tree undergoes extensively remodeling and expansion during puberty, pregnancy, and lactation and, unlike most other organs, the bulk of mammary gland development occurs late, during puberty. An active cell biological debate has focused on lineage commitment to basal- and luminal- epithelial cell fates by epithelial progenitor and stem cells; processes that are also relevant to cancer biology. In this review, we discuss the current understanding of heterogeneity in mammary gland and recent insights obtained through lineage tracing, signaling assays, and organoid cultures. Lastly, we relate these insights to cancer and ongoing efforts to resolve heterogeneity in breast cancer with single-cell RNAseq approaches

Improved determination of VOCs in marine biota by using on-line purge and trap-gas chromatography-mass spectrometry

A Tekmar LSC-2000 Purge and Trap (P&T) apparatus was further modified in order to improve the on-line P&T gas chromatographic etermination of Volatile Organic Compounds (VOCs) in biological tissue. The standard needle sparger of the Tekmar was replaced by a system consisting of two needles (purge gas in- and outlet) and a moisture trap. This modification allows a rapid throughput of samples and minimizes the risk of contamination or losses. Addition of 1-octanol proved successful in eliminating the severe sample foaming that generally occurs when biological material is purged. For separation of the analytes a J&W DB-VRX column (60 m, 0.25 mm i.d., 1.4 µm film) was used, which allowed the elimination of the cryofocusing step prior to injection. The method was tested for 13 priority VOCs and detection limits were obtained ranging from 0.003 ng/g (tetrachloromethane) to 0.16 ng/g (m- and p-xylene) using single ion monitoring-mass spectrometry. The reproducibility was around 15 % for most compounds and the recoveries were better than 80 % for all analytes except 1,1-dichloroethane (59 %).Although the method was originally validated for 13 VOCs, it was found to be applicable for a broader range of VOCs and was tested an eel from the Scheldt estuary. Apart from the priority VOCs several other VOCs turned up rather unexpectedly in these samples. They were identified on the basis of their mass spectra and quantified using selected ion monitoring

Concentration and patterns of PAHs along the salinity gradient of the Scheldt estuary

At MUMM a method was recently developed to determine Polycyclic Aromatic Hydrocarbons (PAHs) in surface waters, even with high particulate matter concentrations, as is the case for the Scheldt Estuary. The method is based on a solid phase extraction with Bakerbond Speedisk C18 cartridges (Baker Inc, Phillipsburg, NJ). After testing this method during a one-year international OSPAR pilot study, the same method was applied for water samples collected for the ENDIS-RISKS program during 2003. Total water concentrations varied between 10 ng/L and 1200 ng/L. Concentrations are tight linked to sources. Fluoranthene was found in the highest concentrations near Antwerp, while in Doel acenaphtylene seemed to be the most dominant compound. The patterns were generally dominated by the lower molecule weight PAHs. There is a clear gradient from Antwerp to the mouth of the estuary near Flushing. Concentrations and PAH patterns were further compared to previous results

Volatile organic compounds in various marine organisms from the southern North Sea

The concentration levels of 12 priority volatile organic compounds (VOCs) were determined in two species of vertebrates and four species of invertebrates from sampling stations in the Southern North Sea, using a modified Tekmar LSC 2000 purge and trap system coupled to GC-MS. In general, concentration levels of VOCs found in this study were of the same order of magnitude as those previously reported in the literature. The concentrations of the chlorinated hydrocarbons (CHCs), with the exception of chloroform, tended to be lower than those of the monocyclic aromatic hydrocarbons (MAHs). The experimental data were statistically evaluated using both cluster and principal component analysis (PCA). From the results of cluster analysis and PCA, no specific groups could be distinguished on the basis of geographical, temporal or biological parameters. However, based on the cluster analysis and the PCA, the VOCs could be divided into three groups, C2-substituted benzenes, CHCs and benzene plus toluene. This division could be related to different types of sources. Finally, it was shown that organisms can be used to monitor the presence of VOCs in the marine environment and the observed concentrations levels were compared with proposed safety levels

Improved determination of VOCs in marine biota by using on-line purge and trap-gas chromatography-mass spectrometry

A Tekmar LSC-2000 Purge and Trap (P&T) apparatus was further modified in order to improve the on-line P&T gas chromatographic etermination of Volatile Organic Compounds (VOCs) in biological tissue. The standard needle sparger of the Tekmar was replaced by a system consisting of two needles (purge gas in- and outlet) and a moisture trap. This modification allows a rapid throughput of samples and minimizes the risk of contamination or losses. Addition of 1-octanol proved successful in eliminating the severe sample foaming that generally occurs when biological material is purged. For separation of the analytes a J&W DB-VRX column (60 m, 0.25 mm i.d., 1.4 µm film) was used, which allowed the elimination of the cryofocusing step prior to injection. The method was tested for 13 priority VOCs and detection limits were obtained ranging from 0.003 ng/g (tetrachloromethane) to 0.16 ng/g (m- and p-xylene) using single ion monitoring-mass spectrometry. The reproducibility was around 15 % for most compounds and the recoveries were better than 80 % for all analytes except 1,1-dichloroethane (59 %).Although the method was originally validated for 13 VOCs, it was found to be applicable for a broader range of VOCs and was tested an eel from the Scheldt estuary. Apart from the priority VOCs several other VOCs turned up rather unexpectedly in these samples. They were identified on the basis of their mass spectra and quantified using selected ion monitoring