Space Division Multiple Access (SDMA): An Editorial Introduction

Wireless Personal Communications -     

On a Distributed Cognitive MAC Protocol for IEEE 802.11s Wireless Mesh Networks

A distributed frequency agile medium access control (MAC) extension to the IEEE 802.11s for the next generation wireless mesh networks is proposed. The introduced protocol enhancements are capable of concurrent deployment of existing frequency opportunities in order to coordinate simultaneous data transmissions. The root concept is mainly based on the deployment of well-known ISM frequency bands, where the legacy 802.11-based wireless equipments operate, as the common control channel in order to establish contemporaneous transmissions. We apply the aforementioned key concept to the IEEE 802.11s common channel framework to attain two important goals: To improve the channel utilization using the concept of cognitive radio, and to lower the access delay. Through extensive event-driven simulations, taking into account primary user appearance in non-ISM frequency bands, performance of the proposed MAC enhancement is evaluated showing its higher efficiency compared to the existing solutions, in addition to its better wireless medium management.     

Quantification of singlet oxygen from hematoporphyrin derivative by electron spin resonance

The mechanism of the generation and the quantitative analysis of singlet oxygen (1O2) formed by the exposure of a hematoporphyrin derivative (HpD) to light was re-evaluated by electron spin resonance (ESR) combined with 2,2,6,6,-tetramethyl-4-piperidine (TMPD). The change from TMPD to 2,2,6,6,-tetramethyl-4-piperidine-N-oxide (TAN) has been reported to depend on singlet oxygen. However, we confirmed that this reagent also react with superoxide anion (O2-) and hydroxyl radicals (OH). Therefore, the reactions between TMPD and 1O2, O2- and OH were re-examined using a kinetic approach. We found that the generation of TAN was proportional to the concentration of TMPD and HpD, as well as to the duration and strength of the illumination. The generation of TAN was not inhibited by dimethyl-sulfoxide (DMSO) or superoxide dismutase (SOD). The reaction rate between TMPD and 1O2 was determined to be 5.0 x 10(-7) M min-1. The generation of 1O2 from HpD was 2.7 x 10(-7) M min-1 under our conditions. The competitive reaction observed between 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and TMPD for O2- or OH shows that TMPD reacts with both forms of active oxygen, but gave no ESR signal. The second-order reaction rate constant of TMPD between O2- and OH was calculated as 73 M-1 s-1 and 1.5 x 10(9) M-1 s-1, respectively. The photochemical generation of 1O2 from methylene blue, another sensitizer, was also demonstrated by this method. These results show that ESR signal of TAN can be used for the highly selective monitoring of 1O2.     

Preparation and Faraday Effect of Fluoroaluminate Glasses Containing Divalent Europium Ions

Fluoroaluminate glasses containing various concentrations of Eu²⁺ were prepared under a reducing atmosphere for the present study, and the wavelength dependence of the Faraday rotation angle was examined. The magnitude of the Verdet constant (V_c) increased as the concentration of Eu²⁺ increased. In addition, the Verdet constant of glasses containing 5 cat.% Eu²⁺ was larger than that of fluoroaluminate glasses containing the same concentration of Tb³⁺ in the wavelength region from 400 to 600 nm. The effective transition wavelength, λ_t, for glasses containing Eu²+ as well as those containing Tb³+ was evaluated based on the Van Vleck and Hebb theory. Factors dominating the Verdet constant of those glasses are discussed in this report.     

Fabrication and Mechanical Properties of Si3N4/Carbon Fiber Composites with Aligned Microstructure Produced by a Seeding and Extrusion Method

Si₃N₄/carbon fiber composites have been produced with and without seeding by an extrusion and sintering process. In both cases the carbon fibers were aligned along the direction of extrusion, but the Si₃N₄ grains were only aligned in the seeded material. The mechanical properties of the specimens showed anisotropy with respect to the grain alignment, with both strength and toughness being highest in the direction parallel to the extruding direction. In this direction the seeded specimen, where both the Si₃N₄ grains and the carbon fibers were aligned, showed both higher fracture toughness and higher fracture strength than the nonseeded specimen where only the fibers were aligned.     

Human colorectal carcinomas specifically accumulate Mr 42,000 ubiquitin-conjugated cytokeratin 8 fragments

Recent studies have shown that various tumor cells accumulate ubiquitin (Ub)-conjugated proteins, the profiles of which differ from those of normal cells. To identify the Ub-conjugated proteins accumulated specifically by human carcinoma cells, a two-dimensional immunoblot analysis of 31 surgically resected human primary colorectal carcinoma tissues was performed using an anti-Ub monoclonal antibody, KM691. Two distinct Mr 42,000 and 45,000 proteins in the Triton X-insoluble fractions of carcinoma tissues reacted with this antibody, whereas only one Mr 45,000 protein reacted in normal tissues. The Mr 42,000 Ub-conjugated proteins were specific to carcinoma tissues from 25 patients (80.6%). One of the purified Mr 42,000 proteins was digested with Achromobacter protease I. This protein was identified as a cytokeratin 8 (CK 8) fragment based on both molecular mass determination and molecular mass searching of Achromobacter protease I-digested fragments of proteins registered in a protein sequence data base. Two-dimensional immunoblot analysis with an anti-CK 8 antibody confirmed that all of the Mr 42,000 proteins were CK 8 degradation products. These results demonstrate that human colorectal carcinomas specifically accumulate Mr 42,000 Ub-conjugated CK 8 fragments. This accumulation was observed frequently not only in advanced (18/22, 81.8%), but also in early stage cases (7/9, 77.8%), suggesting that it occurs even in the early stages of colorectal carcinoma progression.     

Drug delivery system for infectious diseases

Various types of antimicrobial agents have been evolved to inhibit growth of or to kill different microorganisms. In recent years, encapsulation of antimicrobial agents in lipid formulations has been a popular practice in research work related to drug delivery system, although most of the studies are based primary on animal models. The recent developments of lipid formulations of anti-infectious drug (antibiotics, antifungals, and antiviral agents) with longer half-life opens new therapeutic avenues in treating infections. The passive targeting of liposomes to the sites of infection is of great value with respect to clinical application. Liposome entrapment can exchange their pharmacokinetics and, hence reduce their toxicity.     

Nonfluoroscopic guidance for catheter placement into the coronary sinus under direct vision using a balloon-tipped cardioscope

The right atrial posterior septum, including the coronary sinus (CS) ostium, is an important landmark in radiofrequency catheter ablation therapy for supraventricular tachycardia or atrial flutter. The anatomical findings around the CS ostium would be useful to determine a target site or line during catheter ablation. The aim of the study was to test the ability of the imaging catheter to identify structures in the posterior septal area of the right atrium and to evaluate the feasibility of guidance for catheter placement in the CS using a cardioscope that we recently developed. In 12 anesthetized dogs, the cardioscope, consisting of a deflectable 7 Fr fiberoptic endoscope with an inflatable and transparent balloon, was introduced into the right atrium via the femoral vein. The cardioscope was manipulated to observe the right atrial posterior septum. A deflectable electrode catheter was inserted via the jugular vein and positioned in the CS under cardioscopic guidance. In 10 of 12 dogs, the right atrial posterior septum, including the CS ostium, and the tendon of Todaro could be anatomically identified by cardioscopy. It was possible to position an electrode catheter in the CS in all 10 dogs under direct vision without fluoroscopy. But the CS ostium could not be detected in the remaining two dogs, although the cardioscope was placed at as many sites as possible. No complication occurred. The balloon-tipped cardioscope appears to be useful in observing the right atrialposterior septum and in guiding an electrode catheter into the CS.     

Tubulin Photoaffinity Labeling with Biotin‐Tagged Derivatives of Potent Diketopiperazine Antimicrotubule Agents

NPI‐2358 ( 1 ) is a potent antimicrotubule agent that was developed from a natural diketopiperazine, phenylahistin, which is currently in Phase I clinical trials as an anticancer drug. To understand the precise recognition mechanism of tubulin by this agent, we focused on its potent derivative, KPU‐244 ( 2 ), which has been modified with a photoreactive benzophenone structure, and biotin‐tagged KPU‐244 derivatives ( 3 and 4 ), which were designed and synthesized for tubulin photoaffinity labeling. Introduction of the biotin structure at the p′‐position of the benzophenone ring in 2 exhibited reduced, but significant biological activities with tubulin binding, tubulin depolymerization and cytotoxicity in comparison to the parent KPU‐244. Therefore, tubulin photoaffinity labeling studies of biotin‐derivatives 3 and 4 were performed by using Western blotting analysis after photoirradiation with 365 nm UV light. The results indicated that tubulin was covalently labeled by these biotin‐tagged photoprobes. The labeling of compound 4 was competitively inhibited by the addition of diketopiperazine 1 or colchicine, and weakly inhibited by the addition of vinblastine. The results suggest that photoaffinity probe 4 specifically recognizes tubulin at the same binding site as anticancer drug candidate 1 , and this leads to the disruption of microtubules. Probe 4 serves well as a useful chemical probe for potent antimicrotubule diketopiperazines, much like phenylahistin, and it also competes for the colchicine‐binding site.