Biomedical subjects

X S Ling

Publications and source records attributed to X S Ling.

6 recordsLinked to original sources

PubMed2003

Fate of the peak effect in a type-II superconductor: multicriticality in the Bragg-Glass transition.

We have used small-angle neutron scattering (SANS) and ac magnetic susceptibility to investigate the global magnetic field H vs temperature T phase diagram of a Nb single crystal in which a first-order transition of Bragg-glass melting (disordering), a peak effect, and surface superconductivity are all observable. It was found that the disappearance of the peak effect is directly related to a multicritical behavior in the Bragg-glass transition. Four characteristic phase boundary lines have been identified on the H-T plane: a first-order line at high fields, a mean-field-like continuous transition line at low fields, and two continuous transition lines associated with the onset of surface and bulk superconductivity. All four lines are found to meet at a multicritical point.

Journal Article↗

PubMed2003

Fabrication of solid-state nanopores with single-nanometre precision.

Single nanometre-sized pores (nanopores) embedded in an insulating membrane are an exciting new class of nanosensors for rapid electrical detection and characterization of biomolecules. Notable examples include alpha-hemolysin protein nanopores in lipid membranes and solid-state nanopores in Si3N4. Here we report a new technique for fabricating silicon oxide nanopores with single-nanometre precision and direct visual feedback, using state-of-the-art silicon technology and transmission electron microscopy. First, a pore of 20 nm is opened in a silicon membrane by using electron-beam lithography and anisotropic etching. After thermal oxidation, the pore can be reduced to a single-nanometre when it is exposed to a high-energy electron beam. This fluidizes the silicon oxide leading to a shrinking of the small hole due to surface tension. When the electron beam is switched off, the material quenches and retains its shape. This technique dramatically increases the level of control in the fabrication of a wide range of nanodevices.

Crystallization↗

PubMed2001

Diffusion of point defects in two-dimensional colloidal crystals.

Uniform colloidal microspheres dispersed in a solvent will, under appropriate conditions, self-assemble into ordered crystalline structures. Using these colloidal crystals as a model system, a great variety of problems of interest to materials science, physical chemistry, and condensed-matter physics have been investigated during the past two decades. Recently, it has been demonstrated that point defects can be created in two-dimensional colloidal crystals by manipulating individual particles with optical tweezers. Direct imaging of these defects verified that their stable configurations have lower symmetry than the underlying triangular lattice, as predicted by numerical simulations for a number of two-dimensional systems. It was also observed that point defects can dissociate into pairs of well-separated dislocations, a topological excitation especially important in two dimensions. Here we use a similar experimental system to study the dynamics of mono- and di-vacancies in two-dimensional colloidal crystals. We see evidence that the excitation of point defects into dislocation pairs enhances the diffusion of di-vacancies. Moreover, the hopping of the defects does not follow a pure random walk, but exhibits surprising memory effects. We expect the results presented in this work to be relevant for explaining the dynamics of other two-dimensional systems.

Journal Article↗

PubMed2001

Equilibrium configurations and energetics of point defects in two-dimensional colloidal crystals.

We demonstrate a novel method of introducing point defects (mono- and divacancies) in a confined monolayer colloidal crystal by manipulating individual particles with optical tweezers. Digital video microscopy is used to study defect dynamics in real space and time. We verify the numerical predictions that the stable configurations of the defects have reduced symmetry compared to the triangular lattice and discover that in addition they are characterized by distinct topological arrangements of the particles in the defect core. Surprisingly, point defects are thermally excited into separated dislocations, from which we extract the dislocation pair potential.

Journal Article↗

PubMed2001

Superheating and supercooling of vortex matter in a Nb single crystal: direct evidence for a phase transition at the peak effect from neutron diffraction.

We report the first observation of a striking history dependence of the structure function of vortex matter in the peak effect regime in a Nb single crystal by using small angle neutron scattering combined with in situ magnetic susceptibility measurements. Metastable phases of vortex matter, supercooled vortex liquid and superheated vortex solid, have been identified. We interpret our results as direct structural evidence for a first-order vortex solid-liquid transition at the peak effect.

Journal Article↗

PubMed1988

The effects of radiotherapy on the immune system of patients with nasopharyngeal carcinoma.

We report on 123 patients with nasopharyngeal carcinoma whose immune status was measured at the time of diagnosis, the day radiotherapy was completed, and then 2-3 months and 6-8 months after completion of radiotherapy. Immunological tests performed included the lymphocyte transformation test, the erythrocyte-rosette formation test (ERFT), the 29 degrees C erythrocyte-rosette formation test (29 degrees C ERFT), lymphocyte counts (lymphocytes/mm3 and percentage of lymphocytes), levels of serum immunoglobulins (IgG, IgA, IgM), complement (C3) and circulating immune complexes (CIC), the antinuclear antibody test and a skin test using phytohaemagglutinin (PHA). There were statistically significant differences in all tests (except C3) between patients and normal controls. Marked differences were seen in the lymphocyte count, ERFT, and 29 degrees C ERFT after radiotherapy (p less than 0.01). The diameters of induration of the PHA skin tests were less than those before radiotherapy (p less than 0.01). There were higher incidences of recurrence and metastases in the patients with high levels of CIC and low numbers of lymphocytes in the peripheral blood after radiotherapy. Cellular immunity remained at a low level 8 months after radiotherapy.

Antibodies, Antinuclear↗