Target shape dependence in a simple model of receptor-mediated endocytosis and phagocytosis

Phagocytosis and receptor-mediated endocytosis are vitally important particle uptake mechanisms in many cell types, ranging from single-cell organisms to immune cells. In both processes, engulfment by the cell depends critically on both particle shape and orientation. However, most previous theoretical work has focused only on spherical particles and hence disregards the wide-ranging particle shapes occurring in nature, such as those of bacteria. Here, by implementing a simple model in one and two dimensions, we compare and contrast receptor-mediated endocytosis and phagocytosis for a range of biologically relevant shapes, including spheres, ellipsoids, capped cylinders, and hourglasses. We find a whole range of different engulfment behaviors with some ellipsoids engulfing faster than spheres, and that phagocytosis is able to engulf a greater range of target shapes than other types of endocytosis. Further, the 2D model can explain why some nonspherical particles engulf fastest (not at all) when presented to the membrane tip-first (lying flat). Our work reveals how some bacteria may avoid being internalized simply because of their shape, and suggests shapes for optimal drug delivery.Comment: 18 pages, 5 figure

A 100 micro Kelvin bolometer system for SIRTF

Progress toward a prototype of 100 mK bolometric detection system for the Space Infrared Telescope Facility (SIRTF) is described. Two adiabatic demagnetization refrigerators (ADR's) were constructed and used to investigate the capabilities necessary for orbital operation. The first, a laboratory ADR, demonstrated a hold time at 0.1 K of over 12 hours, with temperature stability approx. 3 micro-K RMS achieved by controlling the magnetic field. A durable salt pill and an efficient support system have been demonstrated. A second ADR, the SIRTF flight prototype, has been built and will be flown on a balloon. Techniques for magnetic shielding, low heat leak current leads, and a mechanical heat switch are being developed in this ADR. Plans for construction of 100 mK bolometers are discussed. Three important cosmological investigations which will be carried out by these longest wavelength SIRTF detectors are described

The behavior of the electron density and temperatue at Millstone Hill during the equinox transition study September 1984

The ionospheric electron density and temperature variations is simulated during the equinox transition study in September 1984 and the results are compared with measurements made at Millstone Hill. The agreement between the modeled and measured electron density and temperature for the quiet day (18 September) is very good but there are large differences on the day of the storm (19 September). On the storm day, the measured electron density decreases by a factor of 1.7 over the previous day, while the model density actually increases slightly. The model failure is attributed to an inadequate increase in the ratio of atomic oxygen to molecular neutral densities in the MSIS neutral atmosphere model, for this particular storm. A factor of 3 to 5 increase in the molecular to atomic oxygen density ratio at 300 km is needed to explain the observed decrease in electron density. The effect of vibrationally excited N sub 2 on the electron density were studied and found to be small

The effect of renovation of long-term temperate grassland on N2O emissions and N leaching from contrasting soils

pre-printRenovation of long-term grassland is associated with a peak in soil organic N mineralisation which, coupled with diminished plant N uptake can lead to large gaseous and leaching N losses. This study reports on the effect of ploughing and subsequent N fertilisation on the N2O emissions and DON/NO3− leaching, and evaluates the impact of ploughing technique on the magnitude and profile of N losses. This study was carried out on isolated grassland lysimeters of three Irish soils representing contrasting drainage properties (well-drained Clonakilty, moderately-drained Elton and poorly-drained Rathangan). Lysimeters were manually ploughed simulating conventional (CT) and minimum tillage (MT) as two treatments. Renovation of grassland increased N2O flux to a maximum of 0.9 kg N2O–N ha− 1 from poorly-drained soil over four days after treatment. Although there was no difference between CT and MT in the post-ploughing period, the treatment influenced subsequent N2O after fertiliser applications. Fertilisation remained the major driver of N losses therefore reducing fertilisation rate post-planting to account for N mineralised through grassland renovation could reduce the losses in medium to longer term. Leaching was a significant loss pathway, with the cumulative drainage volume and N leached highly influenced by soil type. Overall, the total N losses (N2O + N leached) were lowest from poorly and moderately draining soil and highest for the well draining soil, reflecting the dominance of leaching on total N losses and the paramount importance of soil properties

Agriculture, meteorology and water quality in Ireland: a regional evaluation of pressures and pathways of nutrient loss to water

peer-reviewedThe main environmental impact of Irish agriculture on surface and ground water quality is the potential transfer of nutrients to water. Soil water dynamics mediate the transport of nutrients to water, and these dynamics in turn depend on agro-meteorological conditions, which show large variations between regions, seasons and years. In this paper we quantify and map the spatio-temporal variability of agro-meteorological factors that control nutrient pressures and pathways of nutrient loss. Subsequently, we evaluate their impact on the water quality of Irish rivers. For nitrogen, pressure and pathways factors coincide in eastern and southern areas, which is reflected in higher nitrate levels of the rivers in these regions. For phosphorus, pathway factors are most pronounced in north-western parts of the country. In south-eastern parts, high pressure factors result in reduced biological water quality. These regional differences require that farm practices be customised to reflect the local risk of nutrient loss to water. Where pathways for phosphorus loss are present almost year-round—as is the case in most of the north-western part of the country—build-up of pressures should be prevented, or ameliorated where already high. In south-eastern areas, spatio-temporal coincidence of nutrient pressures and pathways should be prevented, which poses challenges to grassland management

A projection method for statics and dynamics of lattice spin systems

A method based on Monte Carlo sampling of the probability flows projected onto the subspace of one or more slow variables is proposed for investigation of dynamic and static properties of lattice spin systems. We illustrate the method by applying it, with projection onto the order-parameter subspace, to the three-dimensional 3-state Potts model in equilibrium and to metastable decay in a three-dimensional 3-state kinetic Potts model.Comment: 4 pages, 3 figures, RevTex, final version to appear in Phys. Rev. Let

Digit Ratio (2D:4D) and Amniotic Testosterone and Estradiol: An Attempted Replication of Lutchmaya et al. (2004)

The ratio of length between the second (index) and fourth (ring) fingers (digit ratio or 2D:4D) is frequently employed as a retrospective marker of prenatal sex hormone exposure. Lutchmaya et al. (2004) reported that the ratio of testosterone (T) to estradiol (E) present in second trimester amniotic fluid was negatively correlated with digit ratios for the right hand (but not the left hand) in a sample of 29 children at 2-year follow-up. This observation is frequently cited as evidence for the measure’s validity but has not been replicated. We therefore present the findings of another study of amniotic T and E that did not find evidence for these effects at 4½-year follow-up. The confidence intervals were large, the direction of correlations observed was generally erratic, and the overall findings therefore question the premise that second trimester sex hormones affect the development of digit length ratios in humans

ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo

(abbreviated) We aim to study the inner wind of the well-known AGB star CW Leo. Different diagnostics probing different geometrical scales have pointed toward a non-homogeneous mass-loss process: dust clumps are observed at milli-arcsec scale, a bipolar structure is seen at arcsecond-scale and multi-concentric shells are detected beyond 1". We present the first ALMA Cycle 0 band 9 data around 650 GHz. The full-resolution data have a spatial resolution of 0".42x0".24, allowing us to study the morpho-kinematical structure within ~6". Results: We have detected 25 molecular lines. The emission of all but one line is spatially resolved. The dust and molecular lines are centered around the continuum peak position. The dust emission has an asymmetric distribution with a central peak flux density of ~2 Jy. The molecular emission lines trace different regions in the wind acceleration region and suggest that the wind velocity increases rapidly from about 5 R* almost reaching the terminal velocity at ~11 R*. The channel maps for the brighter lines show a complex structure; specifically for the 13CO J=6-5 line different arcs are detected within the first few arcseconds. The curved structure present in the PV map of the 13CO J=6-5 line can be explained by a spiral structure in the inner wind, probably induced by a binary companion. From modeling the ALMA data, we deduce that the potential orbital axis for the binary system lies at a position angle of ~10-20 deg to the North-East and that the spiral structure is seen almost edge-on. We infer an orbital period of 55 yr and a binary separation of 25 au (or ~8.2 R*). We tentatively estimate that the companion is an unevolved low-mass main-sequence star. The ALMA data hence provide us for the first time with the crucial kinematical link between the dust clumps seen at milli-arcsecond scale and the almost concentric arcs seen at arcsecond scale.Comment: 22 pages, 18 Figures, Astronomy & Astrophysic

A dynamic model of Venus's gravity field

Unlike Earth, long wavelength gravity anomalies and topography correlate well on Venus. Venus's admittance curve from spherical harmonic degree 2 to 18 is inconsistent with either Airy or Pratt isostasy, but is consistent with dynamic support from mantle convection. A model using whole mantle flow and a high viscosity near surface layer overlying a constant viscosity mantle reproduces this admittance curve. On Earth, the effective viscosity deduced from geoid modeling increases by a factor of 300 from the asthenosphere to the lower mantle. These viscosity estimates may be biased by the neglect of lateral variations in mantle viscosity associated with hot plumes and cold subducted slabs. The different effective viscosity profiles for Earth and Venus may reflect their convective styles, with tectonism and mantle heat transport dominated by hot plumes on Venus and by subducted slabs on Earth. Convection at degree 2 appears much stronger on Earth than on Venus. A degree 2 convective structure may be unstable on Venus, but may have been stabilized on Earth by the insulating effects of the Pangean supercontinental assemblage

An Economic analysis of the potential for precision farming in UK cereal production

The results from alternative spatial nitrogen application studies are analysed in economic terms and compared to the costs of precision farming hardware, software and other services for cereal crops in the UK. At current prices, the benefits of variable rate application of nitrogen exceed the returns from a uniform application by an average of £22 ha−1 The cost of the precision farming systems range from £5 to £18 ha−1 depending upon the system chosen for an area of 250 ha. The benefits outweigh the associated costs for cereal farms in excess of 80 ha for the lowest price system to 200–300 ha for the more sophisticated systems. The scale of benefits obtained depends upon the magnitude of the response to the treatment and the proportion of the field that will respond. To be cost effective, a farmed area of 250 ha of cereals, where 30% of the area will respond to variable treatment, requires an increase in crop yield in the responsive areas of between 0·25 and 1.00 t ha−1 (at £65 t−1) for the basic and most expensive precision farming systems, respectively