Influence of van der Waals and Casimir Forces on Electrostatic Torsional Actuators

The influence of van der Waals (vdW) and Casimir forces on the stability of the electrostatic torsional nanoelectromechanical systems (NEMS) actuators is analyzed in the paper. With the consideration of vdW and Casimir effects, the dependence of the critical tilting angle and pull-in voltage on the sizes of structure is investigated. And the influence of vdW torque is compared with that of Casimir torque. The modified coefficients of vdW and Casimir torques on the pull-in voltage are, respectively, calculated. When the gap is sufficiently small, pull-in can still take place with arbitrary small angle perturbation because of the action of vdW and Casimir torques even if there is not electrostatic torque. And the critical pull-in gaps for two cases are, respectively, derived.

Dissociation of egocentric and allocentric spatial processing in prefrontal cortex

Monkeys with lesions of areas 9 and 46 performed three variants of the spatial delayed response (SDR) task. There were no impairments in allocentric spatial memory in which geometrical relationships between environmental cues were used to identify spatial location; thus, memory of a 3D environmental map is intact. In contrast, there were severe impairments in egocentric spatial memory guided by visual or tactile cues that monkeys can relate to their viewing perspective during testing. These results strongly suggest that dorsolateral prefrontal cortex selectively mediates spatial memory tasks that are solved by referencing the location of targets to the body's orientation. (C) 2003 Lippincott Williams Wilkins.

Learning large-scale spatial relationships in a maze and effects of MK-801 on retrieval in the rhesus monkey

Monkeys have strong abilities to remember the visual properties of potential food sources for survival in the nature. The present study demonstrated the first observations of rhesus monkeys learning to solve complex spatial mazes in which routes were guid

Growth kinetics of 1-2 mm and 3-4 mm colonies of Nostoc sphaeroides (Cyanophyta) in outdoor culture

Nostoc sphaeroides Kutzing was cultivated in paddlewheel-driven raceway ponds and the growth kinetics of 1-2 mm and 3-4 mm colonies of N. sphaeroides was studied. The biomass productivities in 2.5 m(2) raceway ponds inoculated with 1-2 mm and 3-4 mm colonies were 5.2 and 0.25 g dry wt m(-2) stop d(-1), respectively. Furthermore, differently sized colonies showed different relative water content, total soluble carbohydrates, chlorophyll a content and density of filaments. This is the first report on mass culture of N. sphaeroides under outdoor conditions.

Effects of Ag on electrical properties of Ag/Ni/p-GaN ohmic contact

Properties of the Ag/Ni/p-GaN structure at different temperatures are studied by Auger electron spectroscopy, scanning electron microscopy and high resolution x-ray diffraction. The effect of Ag in ohmic contact on the crystalline quality is investigated and the optimized value of annealing temperature is reported. The lowest specific contact resistance of 2.5 x 10(-4) Omega cm(2) is obtained at annealing temperature of 550 degrees C.

Layer-by-layer assembly of single-charged ions with a rigid polyampholyte

A novel method to produce multilayer films has been developed by layer-by-layer assembly of single-charged ions and a rigid polyampholyte containing unbalanced charges in each of its repeat units.

Synthesis and characterization of electroactive and biodegradable ABA block copolymer of polylactide and aniline pentamer

A triblock copolymer PLA-b-AP-b-PLA (PAP) of polylactide (PLA) and aniline pentamer (AP) with the unique properties of being both electroactive and biodegradable is synthesized by coupling an electroactive carboxyl-capped AP with two biodegradable bihydroxyl-capped PLAs via a condensation reaction. Three different molecule weight PAP copolymers are prepared. The PAP copolymers exhibit excellent electroactivity similar to the AP and polyaniline, which may stimulate cell proliferation and differentiation. The electrical conductivity of the PAP2 copolymer film (similar to 5 x 10(-6) S/cm) is in the semiconducting region. Transmission electron microscopic results suggest that there is microphase separation of the two block segments in the copolymer, which might contribute to the observed conductivity. The biodegradation and biocompatibility experiments in vitro prove the copolymer is biodegradable and biocompatible. Moreover, these new block copolymer shows good solubility in common organic solvents, leading to the system with excellent processibility. These biodegradable PAP copolymers with electroactive function thus possess the properties that would be potentially used as scaffold materials for neuronal or cardiovascular tissue engineering.

Effect of crosslinking distribution on gas permeability and permselectivity of crosslinked polyimides

Crosslinking modification of polyimide, prepared from 3,3'4,4'-benzophenone tetracarboxyl dianhydride (BTDA) and 2,3,5,6-tetramethyl-1,4-diphenylenediamine (4MPDA), was performed by two methods, putting the polyimide in ambient environment for 4 months, and under UV irradiation for 2 or 8 h. The gas permeation properties of the crosslinked polyimides were investigated. The crosslinked polyimides induced by UV irradiation, in which crosslinking occurs in the surface layer, are of much higher gas permselectivity of hydrogen to nitrogen than that induced by the ambient environment, in which crosslinking takes place in the whole matrix, but their gas permeabilities for hydrogen are similar. (C) 1999 Elsevier Science Ltd. All rights reserved.