Current capabilities and limitations of available stereological techniques

The various methods available for stereological analysis of sectioned material are reviewed with special emphasis on a critical evaluation of their capabilities, advantages and limitations. The review deals with four main topics: (I) Comparison with structural standards; (II) Point counting methods; (III) Image analysis with the scanning microphotometer; (IV) Automatic image analysis based on television systems. It is concluded that each of these approaches has its place, and that the choice essentially depends on the properties of the material and on the nature of the problem.     

Verminderung des Verformungsvermögens bei mehrachsigen Spannungszuständen unter Kriechbeanspruchung

Degradation of the Deformation Capacity under Creep due to Multiaxial States of Stress A method is proposed, which describes the degradation of the uniform true (rupture) strain φ due to the multiaxial stress states in creep. The method is based on the formulas of Siebel which describe the ratios of the uniform true strains in the 3 principle stress directions for any given states of stress: σ_m is the hydrostatic stress. These values for different given stress states are normalized by the principle stress σ_IZV for uniaxial tension with the same amount as for the multiaxial stress states. From such ratios it is possible to find out the real uniform true (rupture) strains φ for the different stress states in taking the uniform true (rupture) strain for uniaxial tension, φ_IBZV, as a basis: The comparison of predicted and tested φ-values proves that the formulas describe the toughness-degradations with the right tendency. For multiaxial states of stress it has to be kept in mind that we have two counterbalancing influences which are on the one hand the reduction of the creep rate due to lower v. Mises equivalent stresses and on the other hand the reduction of the deformation capacity, described above. A model ist proposed to estimate these influences of the states of stress on the creep rupture times.     

Anisotropy in Quasiparticle Density of States in the Vortex State of an Orthorhombic d-Wave Superconductor

The quasiparticle density of states is calculated in the vortex state of an orthorhombic d-wave superconductor as a function of the orientation of the external magnetic field (H ) in the CuO ₂ -plane. Because of the existence of chains oriented along the y-axis in YBCO, its in-plane properties are highly anisotropic and in the superconducting state a predominantly order parameter will also contain a subdominant s-wave admixture allowed by the orthorhombic crystal space group. In a simple anisotropic effective mass model for the band structure and a d + s gap we compute the quasiparticle density of states as a function of the orientation () of H with respect to the a-axis in the CuO ₂ plane. As a function of we find a two fold pattern of behavior with minima at the angles where the Fermi velocity at the nodal momentum is in the direction of the external field. For an untwinned single crystal the resulting anisotropy of the specific heat at low temperatures should be measurable. It is greatly reduced in twinned samples     

Photoactivation of CdSe/ZnS quantum dots embedded in silica colloids

A study of the influence of the local environment on the light-induced luminescence enhancement of CdSe/ZnS quantum dots (QD) embedded in silica colloids that are dispersed in various solvents is presented. The photoluminescence of the embedded QD is enhanced up to a factor of ten upon photoactivation by ultraviolet or visible light. This enhancement is strongly dependent on the local environment. The thickness-dependent permeability of the silica shell covering the QD controls the influence of the solvent on the QD. If foreign ions are present the activation state is stabilized after termination of the activation, whereas in their absence the process is partially reversible. A new qualitative model for the photoactivation of QD in various environments is developed. It comprises light-induced passivation and subsequent oxidation processes. The embedded QD also retain their fluorescence quantum yield inside living cells. Moreover, they can be activated for many hours in living cells by laser radiation in the visible regime.     

Decomposition pressures in the (α + β) fields of the Li-LiH,Li-LiD,and Li-LiT systems

Decomposition (“plateau”) pressures of H₂, D₂, and T₂ over Li-LiH, Li-LiD, and Li-LiT alloys were determined between 600 and 850°C, for pressures ranging from 3 to 460 Torr, and for alloy compositions falling within the (α + β) miscibility gaps. The measurements were carried out separately for each hydrogen isotope using the same lithium sample and experimental procedures. For each system the ln P vs. 1/T data form a pair of linear segments, the intersection of which represents the monotectic temperature (694°C for Li-LiH, 690°C for Li-LiD, and 688°C for Li-LiT). For a given temperature plateau pressures were in the order P_T2 >P_D2 >P_H2. The $\text{D}\text{H}$ and $\text{T}\text{H}$ isotope effects in pressures varied from 1.48 and 1.74 at 600°C to 1.34 and 1.45 at 850°C. The results were used to calculate the standard free energies of formation of solid LiH, LiD, and LiT. The tritium gas used in this study had significant amounts of hydrogen and deuterium. A method for correcting the plateau pressures of this mixture to those of pure tritium is presented.     

A parallel, high-order discontinuous Galerkin code for laminar and turbulent flows

In this study we present a solution method for the compressible Navier-Stokes equations as well as the Reynolds-averaged Navier-Stokes equations (RANS) based on a discontinuous Galerkin (DG) space discretisation. For the turbulent computations we use the standard Wilcox k-ω or the Spalart-Allmaras model in order to close the RANS system. We currently apply either a local discontinuous Galerkin (LDG) or one of the Bassi-Rebay formulations (BR2) for the discretisation of second-order viscous terms. Both approaches (LDG and BR2) can be advanced explicitly as well as implicitly in time by classical integration methods. The boundary is approximated in a continously differentiable fashion by curved elements not to spoil the high-order of accuracy in the interior of the flow field.Computations are performed for the circular cylinder, the flat plate and classical airfoil sections like NACA0012. We compare our obtained results with experimental and computational data as well as analytical (boundary layer) predictions for the flat plate. The excellent parallelisation characteristics of the scheme are demonstrated, achieved by hiding communication latency behind computation.     

Engineering an Artificial T‐Cell Stimulating Matrix for Immunotherapy

T cell therapies require the removal and culture of T cells ex vivo to expand several thousand‐fold. However, these cells often lose the phenotype and cytotoxic functionality for mediating effective therapeutic responses. The extracellular matrix (ECM) has been used to preserve and augment cell phenotype; however, it has not been applied to cellular immunotherapies. Here, a hyaluronic acid (HA)‐based hydrogel is engineered to present the two stimulatory signals required for T‐cell activation—termed an artificial T‐cell stimulating matrix (aTM). It is found that biophysical properties of the aTM—stimulatory ligand density, stiffness, and ECM proteins—potentiate T cell signaling and skew phenotype of both murine and human T cells. Importantly, the combination of the ECM environment and mechanically sensitive TCR signaling from the aTM results in a rapid and robust expansion of rare, antigen‐specific CD8+ T cells. Adoptive transfer of these tumor‐specific cells significantly suppresses tumor growth and improves animal survival compared with T cells stimulated by traditional methods. Beyond immediate immunotherapeutic applications, demonstrating the environment influences the cellular therapeutic product delineates the importance of the ECM and provides a case study of how to engineer ECM‐mimetic materials for therapeutic immune stimulation in the future.     

Loading,unloading, storage,drying, and cleaning of vegetable oil-bearing materials

Handling of various oil-bearing materials and special problems of loading, cleaning, drying, and storage are discussed, along with considerations for preventing quality deterioration during storage.