ABSTRACT
We report a method to controllably alter the diameter of an individual carbon nanotube. The combination of defect formation via electron irradiation and simultaneous resistive heating and electromigration in vacuum causes the nanotube to continuously transform into a high-quality nanotube of successively smaller diameter, as observed by transmission electron microscopy. The process can be halted at any diameter. Electronic transport measurements performed in situ reveal a striking dependence of conductance on nanotube geometry. As the diameter of the nanotube is reduced to near zero into the carbon chain regime, we observe negative differential resistance.
ABSTRACT
We describe interlayer force measurements during prolonged, cyclic telescoping motion of a multiwalled carbon nanotube. The force acting between the core and the outer casing is modulated by the presence of stable defects and generally exhibits ultralow friction, below the measurement limit of 1.4 x 10(-15) N/atom and total dissipation per cycle lower than 0.4 meV/atom. Defects intentionally introduced in the form of dangling bonds lead to temporary mechanical dissipation, but the innate ability of nanotubes to self heal rapidly optimizes the atomic structure and restores smooth motion.
ABSTRACT
We have created a tunable mechanical nanoscale resonator with potential applications in precise mass, force, position, and frequency measurement. The device consists of a specially prepared multiwalled carbon nanotube (MWNT) suspended between a metal electrode and a mobile, piezo-controlled contact. By exploiting the unique telescoping ability of MWNTs, we controllably slide an inner nanotube core from its outer nanotube casing, effectively changing its length and tuning its flexural resonance frequency.
ABSTRACT
We have created insulated C60 nanowire by packing C60 molecules into the interior of insulating boron nitride nanotubes (BNNTs). For small-diameter BNNTs, the wire consists of a linear chain of C60 molecules.With increasing BNNT inner diameter, unusual C60 stacking configurations are obtained (including helical, hollow core, and incommensurate) that are unknown for bulk or thin-film forms of C60.C60 in BNNTs thus presents a model system for studying the properties of dimensionally constrained "silo" crystal structures. For the linear-chain case, we have fused the C60 molecules to form a single-walled carbon nanotube inside the insulating BNNT.
Subject(s)
Diabetes Mellitus/epidemiology , Diabetes Mellitus/prevention & control , Government Agencies/organization & administration , National Health Programs/organization & administration , Canada/epidemiology , Guidelines as Topic , Health Surveys , Humans , Prevalence , Quality Assurance, Health Care , ResearchABSTRACT
This pilot clinical trial was a 15-week, double-blind, controlled, three-way crossover study evaluating cognitive effects of ceranapril in subjects with dementia of the Alzheimer type (age range 50-75 years). Computerized (CNTB) and noncomputerized cognitive test batteries revealed no significant results (p > 0.05). On further analysis of the data, however, a study of longer duration and/or higher dosages may be warranted.
Subject(s)
Alzheimer Disease/drug therapy , Angiotensin-Converting Enzyme Inhibitors/administration & dosage , Organophosphorus Compounds/administration & dosage , Proline/analogs & derivatives , Aged , Alzheimer Disease/psychology , Angiotensin-Converting Enzyme Inhibitors/adverse effects , Dose-Response Relationship, Drug , Double-Blind Method , Female , Humans , Male , Middle Aged , Neuropsychological Tests , Organophosphorus Compounds/adverse effects , Pilot Projects , Proline/administration & dosage , Proline/adverse effectsABSTRACT
The Computerized Neuropsychological Test Battery (CNTB), a new assessment tool for neuropsychopharmacologic research, is based on a neuropsychological approach. While it is based on tests previously shown to be sensitive to subtle changes in neuropsychological functioning, it differs from currently available tools for measuring central nervous system effects of new compounds. It has sensitivity to a broader range of cognitive functioning and is more comprehensive than other measurements in its sampling of neuropsychological functions, providing wider application to diverse clinical populations. The CNTB is valid, reliable, and has two alternative forms. Use of the computer as an expert system maximizes standardization and ease of CNTB administration and data analysis. Using this assessment tool, three groups of subjects were compared: young and elderly neurologically normal subjects and elderly subjects with the dementia syndrome of Alzheimer's disease (AD). The AD subjects' summary score on the CNTB correlated significantly with the Blessed Information Memory Concentration Test score. The CNTB summary score was significantly higher in young subjects than in neurologically normal elderly subjects, demonstrating sensitivity to the effects of aging. The CNTB summary score also was significantly higher in neurologically normal elderly subjects than in elderly subjects with AD dementia.
