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Multiwalled carbon nanotube (MWCNT) atomic force microscope (AFM) probes were fabricated with controlled length using nanomanipulators inside scanning electron microscope. The amplitude-distance responses of MWCNT AFM probes were systematically studied experimentally. Several special characteristics of CNT AFM probes were observed, such as amplitude jump-into-zero, rebounds after the probe already touched the surface and large hysteresis during retraction. Transition from attractive to repulsive regions was also observed when the CNT is long and the amplitude is large. Tapping mode amplitude-distance curves were found to change regularly with the length of the carbon nanotubes and their tilting angle relative to the substrate surface normal. The results were comparable with previous theoretical predictions. Through direct observations by electron microscopes, MWCNT AFM probes were found to bend homogenously even when they were pushed toward the SiO 2wafer for several hundred nanometers after they had touched the surface of the substrate. By analyzing the results obtained from several probes it was found that the MWCNT AFM probes in tapping mode should be suitable for stable operation with proper length and working condition.

Mechanisms of deposition and declogging are considered while formulating a new continuum model for bioconvection in a dilute suspension of motile, negatively geotactic microorganisms in a porous medium. According to research in 1988, bioconvection is the name given to pattern-forming convective motions set up in suspensions of swimming microorganisms. "Negative geotaxis" means that the microorganisms tend to swim against the gravitational force. This paper is motivated by experimental research by Kessler who investigated the effect of porous media on the development of convection instability in algal suspensions. In the model suggested in this paper, the decrease of permeability due to cell adsorption by the porous medium is considered and the influence of this permeability decrease on the development of bioconvection is studied. The existence and stability of a two-dimensional plume in a rectangular enclosure with stress-free sidewalls is investigated. Governing equations include the Darcy law as well as the microorganism conservation equations. A conservative finite-difference scheme is utilized to solve these equations numerically. The analysis of the proposed model reveals that the major factors affecting the development of bioconvection are the initial permeability of the porous medium and the rate of cell deposition. For small permeability, the resistance to the fluid flow is too large, and bioconvection does not develop. If the rate of cell deposition is too large, the number of suspended cells quickly becomes too small because of cell capturing by the porous medium. For this reason, the critical density difference in the top fluid layer cannot be reached, and bioconvection does not develop. [Copyright &y& Elsevier]

We present a simple and optimal experimental scheme for an all-optical production of a sodium spinor Bose-Einstein condensate (BEC). With this scheme, we demonstrate that the number of atoms in a pure BEC can be greatly boosted by a factor of 5 over some widely used schemes in a simple single-beam or crossed-beam optical trap. Our scheme avoids technical challenges associated with some all-optical BEC methods and may be applicable to other optically trappable atomic species. In addition, we discuss an upper limit for evaporative cooling efficiency in all-optical BEC approaches and a good agreement between our theoretical model and experimental data. [ABSTRACT FROM AUTHOR]