Strategies for Controlled Placement of Nanoscale Building Blocks

The capability of placing individual nanoscale building blocks on exact substrate locations in a controlled manner is one of the key requirements to realize future electronic, optical, and magnetic devices and sensors that are composed of such blocks. This article reviews some important advances in the strategies for controlled placement of nanoscale building blocks. In particular, we will overview template assisted placement that utilizes physical, molecular, or electrostatic templates, DNA-programmed assembly, placement using dielectrophoresis, approaches for non-close-packed assembly of spherical particles, and recent development of focused placement schemes including electrostatic funneling, focused placement via molecular gradient patterns, electrodynamic focusing of charged aerosols, and others

A new convertible authenticated encryption scheme with message linkages

In this article, we present an authenticated encryption scheme with message linkages used to deliver a large message. To protect the receiver's benefit, the receiver can easily convert the signature into an ordinary one that can be verified by anyone. Several feasible attacks will be discussed, and the security analysis will prove that none of them can successfully break the proposed scheme. (c) 2006 Elsevier Ltd. All rights reserved

Ethanol modified supercritical fluids extraction of scopoletin and artemisinin from Artemisia annua L

This work studied the supercritical carbon dioxide (SC-CO2) extractions with adding 16.25% ethyl alcohol as a co-solvent to obtain scopoletin and artemisinin from Artemisia annua L. A two-factor central composite experimental design was adopted to determine the optimal operation conditions in extracting the maximal amount of these bioactive compounds. Experimental results indicated that the 289 mu g of scopoletin/g of the feed in dry basis and the 11.6 mg of artemisinin/g of the feed had been obtained at these optimal conditions. Two hours ethanol modified SC-CO2 extractions were superior to 16 h Soxhlet N-hexane extractions in producing more pure artemisinin and scopoletin and the amount of the extracts increased with the density of SC-CO2. A normal phase silica-gel column chromatography to purify artemisinin from the SC-CO2 extract presented that the purity of artemisinin attained 98.2% but with a low recovery of 54.4%. This reduced recovery may be caused by an occurrence of the bridging peroxide atoms of artemisinin reacted with silica-gel molecules during the column purification. (c) 2007 Elsevier B.V. All rights reserved