Hindbrain floor plate of the rat: ultrastructural changes occurring during development

Most of the molecular and experimental studies on the floor plate (FP) have been performed on the FP region extending along the spinal cord. However, little is known about the hindbrain FP. The FP undergoes regional and temporal changes throughout development, but information with respect to the ultrastructural correlate of such changes is missing. The present investigation was focused on the ultrastructural developmental changes occurring in the FP of the rat hindbrain. The FP cells of the hindbrain secrete a material reacting with antibodies against the secretory glycoproteins of the subcommissural organ (AFRU). This antibody was used to perform an ultrastructural immunocytochemical analysis of the rat FP. From E-12 on, there is a progressive increase in the development of the rough endoplasmic reticulum (RER), so that by E-18, it has reached a high degree of hypertrophy. A unique feature of the hindbrain FP cells is the presence of tubular formations and 140-nm vesicles that appear to originate from RER cisternae. The labelling of these two structures with AFRU and Concanavalin A strongly suggests that they are pre-Golgi compartments containing secretory material. Since these structures are present in the basal process and in the apical cell pole of the FP cells, the possibility that they release their content at these sites, is discussed. It is proposed that a secretory mechanism bypassing the Golgi apparatus (constitutive secretion?) operates in the FP cells. The presence of apoptotic cells within the FP of E-20 embryos and newborns suggests that death, and not re-differentiation, is the fate of the FP cells.     

Crystal structures of high affinity human T-cell receptors bound to peptide major histocompatibility complex reveal native diagonal binding geometry

Naturally selected T-cell receptors (TCRs) are characterised by low binding affinities, typically in the range 1-100 microM. Crystal structures of syngeneic TCRs bound to peptide major histocompatibility complex (pMHC) antigens exhibit a conserved mode of binding characterised by a distinct diagonal binding geometry, with poor shape complementarity (SC) between receptor and ligand. Here, we report the structures of three in vitro affinity enhanced TCRs that recognise the pMHC tumour epitope NY-ESO(157-165) (SLLMWITQC). These crystal structures reveal that the docking mode for the high affinity TCRs is identical to that reported for the parental wild-type TCR, with only subtle changes in the mutated complementarity determining regions (CDRs) that form contacts with pMHC; both CDR2 and CDR3 mutations act synergistically to improve the overall affinity. Comparison of free and bound TCR structures for both wild-type and a CDR3 mutant reveal an induced fit mechanism arising from restructuring of CDR3 loops which allows better peptide binding. Overall, an increased interface area, improved SC and additional H-bonding interactions are observed, accounting for the increase in affinity. Most notably, there is a marked increase in the SC for the central methionine and tryptophan peptide motif over the native TCR.     

Discrete particle simulations of solids compaction and conveying in a single‐screw extruder

This paper studies granular flow and compaction behavior of high‐density polyethylene by discrete particle modeling in order to gain greater understanding of the stress distribution within the solids‐conveying zone of a single‐screw extruder. The contact force–displacement model used in the simulations was first validated by simulating uniaxial compression in a batch compaction cell. Subsequently, the discrete particle approach was used to model in 3D the movement of particles within the solids‐inflow and solids‐conveying zone of a 32‐mm single‐screw extruder. Results of the simulations showed that axial pressure development did not increase in an exponential manner, as suggested by continuum models, largely due to the compressibility of the solids. The nature by which pressure developed was shown to be further complicated by the retarding frictional forces of the granular bed, indicating Archimedean transport phenomena close to the feed opening when the head pressure was low and inadequate stress transmission occurred along the screw. In the cross‐channel direction, the anisotropic stress field predicted found that the highest pressure in the screw channel was located at the screw root, while the lowest pressure corresponded to the retreating flight. The results were subsequently discussed in comparison to available continuum models. POLYM. ENG. SCI., 48:62–73, 2008. © 2007 Society of Plastics Engineers     

An overlapping Yee finite‐difference time‐domain method for material interfaces between anisotropic dielectrics and general dispersive or perfect electric conductor media

A novel stable anisotropic finite‐difference time‐domain (FDTD) algorithm based on the overlapping cells is developed for solving Maxwell's equations of electrodynamics in anisotropic media with interfaces between different types of materials, such as the interface between anisotropic dielectrics and dispersive medium or perfect electric conductor (PEC). The previous proposed conventional anisotropic FDTD methods suffer from the late‐time instability due to the extrapolation of the field components near the material interface. The proposed anisotropic overlapping Yee FDTD method is stable, as it relies on the overlapping cells to provide the collocated field values without any interpolation or extrapolation. Our method has been applied to simulate electromagnetic invisibility cloaking devices with both anisotropic dielectrics and PEC included in the computational domain. Numerical results and eigenvalue analysis confirm that the conventional anisotropic FDTD method is weakly unstable, whereas our method is stable. Copyright © 2013 John Wiley & Sons, Ltd.     

Determining the collision properties of semi-crystalline and amorphous thermoplastics for DEM simulations of solids transport in an extruder

To improve application of the distinct element method (DEM) to polymer processing applications it was necessary to evaluate the contact mechanics of a selection of commonly used polymers. The contact behaviors of high-density polyethylene (HDPE), polystyrene (PS) and polycarbonate (PC) were revealed in this paper from a series of impact studies where spherical polymeric particles struck a steel anvil at various angles of incidence and impact velocity. The coefficients of restitution and friction were calculated from high-speed video analysis of individual impacts. The collected data was used to evaluate the relevance of several popular normal contact force-displacement models to determine their suitability for the tested semi-crystalline and glassy polymers. The models considered were those proposed by Walton and Braun [1986. Viscosity, granular-temperature, and stress calculations for shearing assemblies of inelastic, frictional disks. Journal of Rheology 30, 949-980], with constant (WBCE) and variable (WBVE) normal restitution coefficient, and Thornton [1997. Coefficient of restitution for collinear collisions of elastic-perfectly plastic spheres. Journal of Applied Mechanics 64, 383-386], based on elastic-plastic collisions. Comparison of the impact data with DEM simulations using the various contact force-displacement models revealed that the WBVE model provides the best overall agreement with the viscoelastic-fully plastic behavior of HDPE, while the almost purely elastic nature of PC and PS agreed well with all three models studied in this paper. The influence of the normal force-displacement models on the solids transport zone of an extruder was subsequently discussed based on the findings from the impact study.     

Overlapping Yee FDTD Method on Nonorthogonal Grids

We propose a new overlapping Yee (OY) method for solving time-domain Maxwell’s equations on nonorthogonal grids. The proposed method is a direct extension of the Finite-Difference Time-Domain (FDTD) method to irregular grids. The OY algorithm is stable and maintains second-order accuracy of the original FDTD method, and it overcomes the late-time instability of the previous FDTD algorithms on nonorthogonal grids. Numerical examples are presented to illustrate the accuracy, stability, convergence and efficiency of the OY method.     

Size Segregation of Nickel Pellets Flowing into a Packed Bed

The size segregation of nickel pellets fed to a packed bed has been measured with mixtures of sizes ranging from less than 1 mm to about 10 mm. The pellet mixture is fed to one side of a rectangular cell and then samples are removed from different lateral positions in the cell for screen analysis. During the feeding process the finer pellets tend to percolate vertically downwards while the larger pellets tend to roll down the sloping surface of the bed. The resulting segregation has been correlated with the size distribution of the feed pellets and the lateral position in the cell, using polynomial equations with three or four adjustable coefficients.     

Isocitrate lyase localisation in Saccharomyces cerevisiae cells

The isocitrate lyase from Saccharomyces cerevisiae was only located in the cell cytoplasm. This protein was found not to be associated with cell organelles, even under growth conditions that induce peroxisome proliferation. This conclusion is supported by experiments carried out by damaging the protoplast plasma membrane with DEAE-dextran, by differential centrifugation of osmotically lysed protoplast and by using the green fluorescent protein (GFP) of Aequorea victoria as a reporter fusion tag to localise the subcellular compartment to which isocitrate lyase is targeted.     

Pilot ignition of building materials by radiation

The ignition characteristics of building materials influence the spread of fire from one building to another. With some materials tested, there are significant differences in radiation levels to which materials can be safely exposed.     

Application of Post’s formula to optical pulse propagation in dispersive media

In this paper we consider the propagation of optical pulses in dielectric media with nontrivial dispersion relations. In particular, we implement Post’s Laplace transform formula to invert in time the Fourier–Laplace space coefficients which arise from the joint space solution of the optical dispersive wave equation. Due to the inefficiency of a direct application of this formula, we have considered and present here two more efficient implementations. In the first, the Gaver–Post method, we utilize the well known Gaver functionals but store intermediate calculations to improve efficiency. The second, the Bell–Post method, involves an analytic reformulation of Post’s formula such that knowledge of the dispersion relation and its derivatives are sufficient to invert the coefficients from Laplace space to time. Unlike other approaches to the dispersive wave equation which utilize a Debye–Lorentzian assumption for the dispersion relation, our algorithm is applicable to general Maxwell-Hopkinson dielectrics. Moreover, we formulate the approach in terms of the Fourier–Laplace coefficients which are characteristic of a dispersive medium but are independent of the initial pulse profile. They thus can be precomputed and utilized when necessary in a real-time system. Finally, we present an illustration of the method applied to optical pulse propagation in a free space and in two materials with Cole-type dispersion relations, room temperature ionic liquid (RTIL) hexafluorophosphate and brain white matter. From an analysis of these examples, we find that both methods perform better than a standard Post-formula implementation. The Bell–Post method is the more robust of the two, while the Gaver–Post is more efficient at high precision and Post formula approximation orders.