17,430 research outputs found
Does the motor system need intermittent control?
Explanation of motor control is dominated by continuous neurophysiological pathways (e.g. trans-cortical, spinal) and the continuous control paradigm. Using new theoretical development, methodology and evidence, we propose intermittent control, which incorporates a serial ballistic process within the main feedback loop, provides a more general and more accurate paradigm necessary to explain attributes highly advantageous for competitive survival and performance
Experiments in randomly agitated granular assemblies close to the jamming transition
We present here the preliminary results obtained for two experiments on
randomly agitated granular assemblies using a novel way of shaking. First we
discuss the transport properties of a 2D model system undergoing classical
shaking that show the importance of large scale dynamics for this type of
agitation and offer a local view of the microscopic motions of a grain. We then
develop a new way of vibrating the system allowing for random accelerations
smaller than gravity. Using this method we study the evolution of the free
surface as well as results from a light scattering method for a 3D model
system. The final aim of these experiments is to investigate the ideas of
effective temperature on the one hand as a function of inherent states and on
the other hand using fluctuation dissipation relations.Comment: Contribution to the volume "Unifying Concepts in Granular Media and
Glasses", edt.s A. Coniglio, A. Fierro, H.J. Herrmann and M. Nicodem
Nanoscale intermittent contact-scanning electrochemical microscopy
A major theme in scanning electrochemical microscopy (SECM) is a methodology for nanoscale imaging with distance control and positional feedback of the tip. We report the expansion of intermittent contact (IC)-SECM to the nanoscale, using disk-type Pt nanoelectrodes prepared using the laser-puller sealing method. The Pt was exposed using a focused ion beam milling procedure to cut the end of the electrode to a well-defined glass sheath radius, which could also be used to reshape the tips to reduce the size of the glass sheath. This produced nanoelectrodes that were slightly recessed, which was optimal for IC-SECM on the nanoscale, as it served to protect the active part of the tip. A combination of finite element method simulations, steady-state voltammetry and scanning electron microscopy for the measurement of critical dimensions, was used to estimate Pt recession depth. With this knowledge, the tip-substrate alignment could be further estimated by tip approach curve measurements. IC-SECM has been implemented by using a piezo-bender actuator for the detection of damping of the oscillation amplitude of the tip, when IC occurs, which was used as a tip-position feedback mechanism. The piezo-bender actuator improves significantly on the performance of our previous setup for IC-SECM, as the force acting on the sample due to the tip is greatly reduced, allowing studies with more delicate tips. The capability of IC-SECM is illustrated with studies of a model electrode (metal/glass) substrate
Wearing a single DNA molecule with an AFM tip
While the fundamental limit on the resolution achieved in an atomic force
microscope (AFM) is clearly related to the tip radius, the fact that the tip
can creep and/or wear during an experiment is often ignored. This is mainly due
to the difficulty in characterizing the tip, and in particular a lack of
reliable methods that can achieve this in situ. Here, we provide an in situ
method to characterize the tip radius and monitor tip creep and/or wear and
biomolecular sample wear in ambient dynamic AFM. This is achieved by monitoring
the dynamics of the cantilever and the critical free amplitude to observe a
switch from the attractive to the repulsive regime. The method is exemplified
on the mechanically heterogeneous sample of single DNA molecules bound to mica
mineral surfaces. Simultaneous monitoring of apparent height and width of
single DNA molecules while detecting variations in the tip radius R as small as
one nanometer are demonstrated. The yield stress can be readily exceeded for
sharp tips (R10nm). The ability to
know the AFM tip radius in situ and in real-time opens up the future for
quantitative nanoscale materials properties determination at the highest
possible spatial resolution.Comment: 26 pages, 6 figure
The P scales: level descriptors P1 to P8
"These are the level descriptors for pupils working below
level 1 of the national curriculum... To support teachers in making judgements about pupils’ attainment below level 1 of the national curriculum" - Back cover.
This booklet is part of the DVD and print booklet package
'Using the P scales: assessing, moderating and reporting
pupil attainment at levels P1 to P8' (QCA/09/4060
Applications of AFM in pharmaceutical sciences
Atomic force microscopy (AFM) is a high-resolution imaging technique that uses a small probe (tip and cantilever) to provide topographical information on surfaces in air or in liquid media. By pushing the tip into the surface or by pulling it away, nanomechanical data such as compliance (stiffness, Young’s Modulus) or adhesion, respectively, may be obtained and can also be presented visually in the form of maps displayed alongside topography images. This chapter outlines the principles of operation of AFM, describing some of the important imaging modes and then focuses on the use of the technique for pharmaceutical research. Areas include tablet coating and dissolution, crystal growth and polymorphism, particles and fibres, nanomedicine, nanotoxicology, drug-protein and protein-protein interactions, live cells, bacterial biofilms and viruses. Specific examples include mapping of ligand-receptor binding on cell surfaces, studies of protein-protein interactions to provide kinetic information and the potential of AFM to be used as an early diagnostic tool for cancer and other diseases. Many of these reported investigations are from 2011-2014, both from the literature and a few selected studies from the authors’ laboratories
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