Pattern forming instability induced by light in pure and dye-doped nematic liquid crystals

We study theoretically the instabilities induced by a linearly polarized ordinary light wave incident at a small oblique angle on a thin layer of homeotropically oriented nematic liquid crystal with special emphasis on the dye-doped case. The spatially periodic Hopf bifurcation that occurs as the secondary instability after the stationary Freedericksz transition is analyzed.Comment: 8 pages, 7 figures, LaTeX, accepted to Phys. Rev.

Routine immunofluorescent and histochemical analysis of bone marrow involvement of lymphoma/leukaemia: the use of cryostat sections.

Enzyme histochemical and immunohistological (immuno-fluorescence and -peroxidase) techniques have been routinely used for investigating over 70 normal and pathological bone marrow samples. This recently standardized diagnostic procedure is very quick and can be performed in a few hours. In 6 cases the clinical diagnosis of leukaemia/lymphoma has become apparent only after the immunohistological analysis of the bone marrow. In 6 other cases the information about the staging of B cell malignancies was superior in the frozen biopsies to the paraffin embedded preparations. Amongst many other features the monoclonality of B CLL/lymphomas, the special features of B CLL infiltrates (RFA-1+, Leu-1+, HLA-DR+, SmIg+), follicular lymphoma deposits (containing follicular dendritic cells) and non-T, non-B acute lymphoblastic leukaemic blasts (terminal transferase+, HLA-DR+) as well as the sometimes conspicuous presence of infiltrating normal T cells could be clearly and reproducibly demonstrated

Orientational instabilities in nematics with weak anchoring under combined action of steady flow and external fields

We study the homogeneous and the spatially periodic instabilities in a nematic liquid crystal layer subjected to steady plane {\em Couette} or {\em Poiseuille} flow. The initial director orientation is perpendicular to the flow plane. Weak anchoring at the confining plates and the influence of the external {\em electric} and/or {\em magnetic} field are taken into account. Approximate expressions for the critical shear rate are presented and compared with semi-analytical solutions in case of Couette flow and numerical solutions of the full set of nematodynamic equations for Poiseuille flow. In particular the dependence of the type of instability and the threshold on the azimuthal and the polar anchoring strength and external fields is analysed.Comment: 12 pages, 6 figure

Variable Corticosteroid Sensitivity of Thymic Cortex and Medullary Peripheral-type Lymphoid Tissue in Myasthenia Gravis Patients: Structural and Functional Effects

The thymus has been studied in myasthenia gravis patients to assess the effects of previous immunosuppresslon on total yields of cell suspension, immunohistology and culture responses. The reduction in cell yields by pretreatment with corticosteroid was very variable. In 16 of 32 cases, cortical, medullary and total cell numbers were all greatly reduced (‘depleted cases'), whereas in the others, they were within or near the typical range for untreated myasthenics. Cortical thymocytes were even more depleted than precursor thymic blasts. Thus the interpatient differences in sensitivity to corticosteroid recently described for mature T cells also affected immature cortical thymocytes and their differentiating medullary progeny.In the medulla, mature (CD3+)T lymphocytes and germinal centres were enriched by the loss of cortex and appeared relatively healthy, but somewhat depopulated. Concomitantly, in-vitro T-cell responses to acetylcholine receptor (AChR) and production of anti-A ChR antibody and total IgG by thymic cells were usually well within the typical range (assessed per 106 cells). Moreover, the total productivity of the entire thymus was reduced almost entirely by the cellular depopulation rather than by decreased function per surviving cell. Thus the main actions of this alternate day therapy with corticosteroids were apparently on total peripheral cell numbers, and perhaps on activated cells and effector mechanisms too, and its thymic effects were inessentia

High throughput particle analysis: combining dielectrophoretic particle focussing with confocal optical detection

A microflow cytometer has been fabricated that detects and counts fluorescent particles flowing through a microchannel at a high speed based upon their fluorescence emission intensity. Dielectrophoresis is used to continuously focus particles within the flowing fluid stream into the centre of the device, which is 40 μm high and 250 μm wide. The method ensures that all the particles pass through an interrogation region approximately 5 μm in diameter, which is created by focusing a beam of light into a spot. The functioning of the device was demonstrated by detecting and counting fluorescent latex particles at a rate of up to 250 particles/s. A mixture of three different populations of latex particle was used, each sub-population with a distinct level of fluorescent intensity. The device was evaluated by comparison with a conventional fluorescent activated cell sorter (FACS) and numerical simulation demonstrated that for 6 mico m beads, and for this design of chip the theoretical throughput is of the order of 1000 particles/s (corresponding to a particle velocty of 1 mm/s)

Spatial point process theory

No abstract

Anisotropy of superconducting MgB2 as seen in electron spin resonance and magnetization data

We have observed the conduction electron spin resonance (CESR) in fine powders of MgB2 both in the superconducting and normal states. The Pauli susceptibility is chi_s=2.0*10^{-5} emu/mole in the temperature range of 450 to 600 K. The spin relaxation rate has an anomalous temperature dependence. The CESR measured below T_c at several frequencies suggests that MgB_2 is a strongly anisotropic superconductor with the upper critical field, H_c2, ranging between 2 and 16 T. The high-field reversible magnetization data of a randomly oriented powder sample are well described assuming that MgB_2 is an anisotropic superconductor with H_c2^{ab} / H_{c2}^{c} \approx 6--9.Comment: 4 pages, 4 eps figure