Bibliothek

Notizen: The quark propagator in massless quantum chromodynamics (QCD) is analyzed using the gauge technique. In both the Feynman and Landau gauges with a Pauli–Villars cutoff, a chirally symmetric solution is found, while a nonsymmetric solution appears at a critical coupling λc〉0. As the cutoff is removed, λc tends to 0 but the nonsymmetric solution vanishes in the continuum limit, so that chiral symmetry is then restored.

Notizen: Summary. A novel protocol is described which has been developed for immunotherapy in unexplained recurrent miscarriage. This is based on a single intravenous infusion with isolated placental trophoblast plasma membrane vesicle preparations. Clinical experience gained with this approach is described. A total of 16/21 (76%) patients who subsequently had pregnancies have now achieved a live birth or are currently pregnant at greater than 28 weeks gestation.

Notizen: Summary. The distribution, morphology and antigen expression of endometrial glands, uterine vessels and fetal trophoblast have been studied in third trimester placental bed tissues with a panel of monoclonal antibodies in immunohistochemical techniques. Residual endometrial glands were numerous but often were attenuated or compressed and could only be identified clearly with epithelial cell markers. These glands must be clearly distinguished from vessels and trophoblast in immunological studies of cells in the placental bed. The changing pattern of antigen expression of both maternal glands and fetal trophoblast in placental bed tissues may indicate a form of local regulation of gene expression.

Notizen: Optical tuning of an epitaxial, all-semiconductor optical interference filter is reported. The filter is a high reflector composed of alternating, strained layers of GaP (360 A(ring)) and GaAs0.2P0.8 (360 A(ring)) grown by metalorganic chemical vapor deposition. With low optical power, these reflectors exhibit reflectances up to 90% at 510 nm over a 10-nm bandwidth. With absorbed optical pulses of energy density 3 mJ/cm2, this high-reflectance zone can be blue shifted by 20 A(ring). As a result, very large changes in reflectance can be produced. The effect is interpreted as a plasma-induced refractive index depression in a semiconductor superlattice. Furthermore, the layer strain enhances the optically induced index change of the high reflector compared to that in bulk materials.

Notizen: A series of experiments was performed with an Applied-B ion diode on the Particle Beam Fusion Accelerator-I, with peak voltage, current, and power of approximately 1.8 MV, 6 MA, and 6 TW, respectively. The purpose of these experiments was to explore issues of scaling of Applied-B diode operation from the sub-TW level on single module accelerators to the multi-TW level on a low impedance, self-magnetically insulated, multimodule accelerator. This is an essential step in the development of the 100-TW level light ion beam driver required for inertial confinement fusion. The accelerator and the diode are viewed as a whole because the power pulse delivered by the 36 imperfectly synchronized magnetically insulated transmission lines to the single diode affects module addition, diode operation, and ion beam focusability. We studied electrical coupling between the accelerator and the diode, power flow symmetry, the ionic composition of the beam, and the focusability of the proton component of the beam. Scaling of the diode impedance behavior and beam quality with electrical drive power is obtained from comparison with lower-power experiments.The diode impedance lifetime was about 10 ns, several times shorter than for lower-power experiments. Azimuthal and top-to-bottom variations of the diode and ion currents were found to be approximately ±10%, compared with an estimated requirement of 5%–7% uniformity to avoid focal blurring by self-magnetic field effects. The ion production efficiency was 80%–90%. However, only 50%±10% of the ion current was carried by protons; the balance was carried by multiply charged carbon and oxygen ions. Activation measurements showed a proton beam energy of approximately 50 kJ. A gas cell filled with 5 Torr of argon was used for beam transport. The macroscopic divergence was 15±10 mrad and the microscopic divergence was 20±15 mrad, values that are similar to those from lower-power experiments. A model of beam focusing is formulated that predicts the proton charge focused onto 0.47-cm radius lithium targets, taking into account beam purity, magnetic bending, small-angle multiple scattering, and intrinsic divergence. The model results and activation measurements of the number of protons focused onto targets agree, and indicate that the spatially averaged (over about 3 cm2) peak focal power was about 0.5 TW/cm.2 The most important limitations on power concentration were found to be the low proton content of the beam, the short impedance lifetime of the diode, and the asymmetric current feed of the accelerator. The short impedance lifetime limited the power coupled to the diode, and caused the voltage at peak ion power to be low, which exacerbates the small-angle scattering problem. The asymmetric feed caused focal blurring through nonuniform self-magnetic bending. At least partly because of the experience gained with low impedance beams during these experiments, the next generation accelerator, the 100-TW Particle Beam Fusion Accelerator-II, has been configured to produce a 25–30-MV Li+ beam rather than a 5-MV proton beam. off

Notizen: We describe a normal incidence grating spectrometer for use in inverse photoemission studies of surfaces. We show that by operating in a configuration where the source and image are displaced from the Rowland Circle it is possible to construct a useful spectrometer that can be attached to any existing surface science chamber. The device covers the range 10–30 eV in photon energy with a typical energy resolution of 150 meV. Capable of operating with relatively low incident currents, this instrument will be an excellent choice for spin-polarized inverse photoemission experiments.

Notizen: A differential optical reflectivity measurement technique for freestanding films is presented. The system is highly sensitive to changes in the polarization state of the reflected light. The method is used to study the evolution of an optically anisotropic liquid crystalline structure with temperature. In addition we present a reflectivity method for determining the film thickness for films consisting of two to hundreds of layers. © 2000 American Institute of Physics.

Notizen: We compute the braiding for the "principal gradation" of Uq(sl2&dbgcaret;) for |q|=1 from first principles, starting from the idea of a rigid braided tensor category. It is not necessary to assume either the crossing or the unitarity condition from S-matrix theory. We demonstrate the uniqueness of the normalization of the braiding under certain analyticity assumptions, and show that its convergence is critically dependent on the number theoretic properties of the number τ in the deformation parameter q=e2πiτ. We also examine the convergence using probability, assuming a uniform distribution for q on the unit circle. © 2001 American Institute of Physics.

Notizen: The incidence of thrombocythaemia (a platelet count 〉600×l09/l) in a 10-year survey was 7 per 106 population per year (R. M. Pettit, personal communication). It is generally a disease of late middle age, but a second population of young and mainly female patients has been described (Hoagland & Silverstein 1978). An increased platelet count can be secondary (after splenec-tomy, associated with inflammation, malignancy or iron deficiency) or due to a primary myeloproliferative disorder. We describe four patients in whom a series of miscarriages before 20 weeks gestation appears associated with thrombocythaemia and estimate the prevalence of this association in patients with unexplained repeated miscarriage.