Settling the bound on the rectilinear link radius of a simple rectilinear polygon

We improve the best known bound on the rectilinear link radius of a simple rectilinear polygon with respect to its rectilinear link diameter. The new bound is tight and is compatible with the known bound on the (regular) link radius of a (regular) simple polygon with respect to its (regular) link diameter. The previous bound on the rectilinear link radius of a simple rectilinear polygon was proven by Nilsson and Schuierer in 1991.     

Selective cytotoxic effect of ZnO nanoparticles on glioma cells

In this study we examined the cytotoxic effect of ZnO nanoparticles on various human cancer and normal cells. We found that the ZnO nanoparticles exerted a cytotoxic effect on the human glioma cell lines A172, U87, LNZ308, LN18, and LN229, whereas no cytotoxic effect was observed on normal human astrocytes. Similarly, the ZnO nanoparticles induced cell death in breast and prostate cancer cell lines while no major effect was observed in the respective normal breast and prostate cell lines. Using the fluorescent dye 2,7-dichlorofluorescein diacetate, we found that treatment of the glioma cells with ZnO nanoparticles induced a large increase in the generation of reactive oxygen species (ROS) and treatment of the cells with N-acetyl cysteine decreased the cytotoxic effect of the ZnO nanoparticles. In contrast, a smaller effect on ROS generation was observed in the normal astrocytes. These results suggest that ZnO nanoparticles may be employed as a selective cytotoxic agent for the eradication of cancer cells.     

Selective Cerebral Catheterization

This paper describes a new method for selective cerebral catheterization based on the Pod catheter [6], [7], guided and propelled by means of external magnetic fields. The principles of the Pod catheter, and the necessary equipment are described, and conclusions are drawn from experiments with a glass model. The middle cerebral artery was catheterized selectively, and cytotoxic material was injected into it to treat a malignant tumor of the brain hemisphere.     

A Scheme for Computing Minimum Covers within?Simple Regions

Let X be a simple region (e.g., a simple polygon), and let Q be a set of points in X. Let O be a convex object, such as a disk, a square, or an equilateral triangle. We present a scheme for computing a minimum cover of Q, consisting of homothets of O contained in X. In particular, a minimum disk cover of Q with respect to X, can be computed in polynomial time.     

Ir Diffusion Barriers in Ni/Au Ohmic Contacts to <Emphasis Type="Italic">p</Emphasis>-Type CuCrO<Subscript>2</Subscript>

The use of Ir diffusion barriers in Ni/Au-based Ohmic contacts to p-type CuCrO₂ layers was investigated. A specific contact resistance of ~5 × 10⁻⁴ Ω cm² was achieved after annealing at 500°C for the Ir-containing contacts, and the contacts were rectifying for lower anneal temperatures. In this case, the contact resistance was basically independent of the measurement temperature, indicating that tunneling is the dominant transport mechanism in the contacts. The morphology for the Ir-containing contacts was still smooth at 500°C although Auger electron spectroscopy depth profiling showed that some of the nickel had diffused to the surface and had oxidized. Contacts annealed at 800°C showed that some copper and most of the nickel had diffused to the surface and oxidized. The presence of the Ir diffusion barrier does increase the thermal stability of the contacts by ∼200°C compared to conventional Ni/Au contacts. By contrast, the use of other materials such as TaN, ZrN, and W₂B₅ as the diffusion barrier led to poorer thermal stability, with the contact resistance increasing sharply above 400°C.     

Surface Dynamics vs. Adhesion in Oxygen Plasma Treated Polyolefins

Polyethylene (PE) and polypropylene (PP) were oxygen plasma treated and aged in carefully reproducible conditions. The effect of aging on the surface chemistry, wettability and adhesion were studied using a combination of techniques: contact angle measurements, XPS, SSIMS, adhesion tests (shear and pull).

PE was found to be relatively insensitive to aging both in terms of wettability and adhesion, due to crosslinking during plasma treatment, which is likely to reduce macromolecular mobility within the surface layer.

In the case of PP, dramatic decreases of wettability occur with time, due to macromolecular motions leading to minimization of oxygen-containing functions at the surface. This behavior was shown to affect the adhesion performance of treated PP.     

AlGaN/GaN-based diodes and gateless HEMTs for gas and chemical sensing

The characteristics of Pt/GaN Schottky diodes and Sc/sub 2/O/sub 3//AlGaN/GaN metal-oxide semiconductor (MOS) diodes as hydrogen and ethylene gas sensors and of gateless AlGaN/GaN high-electron mobility transistors (HEMTs) as polar liquid sensors are reported. At 25/spl deg/C, a change in forward current of /spl sim/6 mA at a bias of 2 V was obtained in the MOS diodes in response to a change in ambient from pure N/sub 2/ to 10% H/sub 2// 90% N/sub 2/. This is approximately double the change in forward current obtained in Pt/GaN Schottky diodes measured under the same conditions. The mechanism appears to be formation of a dipole layer at the oxide/GaN interface that screens some of the piezo-induced channel charge. The MOS-diode response time is limited by the mass transport of gas into the test chamber and not by the diffusion of atomic hydrogen through the metal/oxide stack, even at 25/spl deg/C. Gateless AlGaN/GaN HEMT structures exhibit large changes in source-drain current upon exposing the gate region to various polar liquids, including block co-polymer solutions. The polar nature of some of these polymer chains lead to a change of surface charges in gate region on the HEMT, producing a change in surface potential at the semiconductor/liquid interface. The nitride sensors appear to be promising for a wide range of chemicals, combustion gases and liquids.     

Investigation of the effect of temperature during off-state degradation of AlGaN/GaN High Electron Mobility Transistors

AlGaN/GaN High Electron Mobility Transistors were found to exhibit a negative temperature dependence of the critical voltage (V_CRI) for irreversible device degradation to occur during bias-stressing. At elevated temperatures, devices exhibited similar gate leakage currents before and after biasing to V_CRI, independent of both stress temperature and critical voltage. Though no crack formation was observed after stress, cross-sectional TEM indicates a breakdown in the oxide interfacial layer due to high reverse gate bias.     

Selective dry etching of (Sc2O3)x(Ga2O3)1−x gate dielectrics and surface passivation films on GaN

(Sc₂O₃)_x(Ga₂O₃)_1?x films grown by molecular beam epitaxy show promise for use as surface passivation layers and gate dielectrics on GaN-based high electron mobility transistors. Completely selective, low-damage, dry etching of (Sc₂O₃)_x(Ga₂O₃)_1?x films with respect to GaN can be achieved with low-power inductively coupled plasmas of CH₄/H₂/Ar with etch rates in the range 200–300 Å/min. The incident ion energies are of order 100 eV, and no roughening of the underlying GaN was observed under these conditions. Similar etch rates were obtained with Cl₂/Ar discharges under the same conditions, but GaN showed rates almost an order of magnitude higher.