Mechanical Drift Research Articles

What will replace the mercury sphygmomanometer?

Mercury sphygmomanometers are gradually being phased out, not because of any technological advances but because of environmental concerns. While mercury is still accepted as the 'gold standard' for routine clinical measurement, it suffers from two deficiencies: poor observer technique, and problems due to poor maintenance of the devices. At the same time, there is no generally accepted alternative; the most widely advocated candidates are aneroid or oscillometric devices. Oscillometric devices have the advantages of eliminating observer error and mechanical drift, but it is suggested that the inherent limitations of the oscillometric method mean that it cannot become the gold standard for clinical measurement in individual patients. Aneroid monitors have been found in practice to be frequently deficient, and are subject to the same deficiencies in observer technique as mercury devices. Two possible but so far untested techniques are a 'hybrid' sphygmomanometer, whereby the mercury column is replaced by an electronic transducer and display, and the wideband recording technique, which has the potential of using the same basic principle as the auscultatory technique, while eliminating the human observer.

Dynamic confocal imaging in acute brain slices and organotypic slice cultures using a spectral confocal microscope with single photon excitation.

Confocal imaging in living brain slices allows the resolution of submicrometre structures of nerve cells, glia and brain vessels. Imaging living brain slices is in many respects different from conventional fixed histological preparations for which confocal microscopes were designed originally. Several problems (i.e. mechanical and thermal drift, and autofluorescence) resulting from the optical and structural properties of brain slices are discussed. Fluorescent indicators may be used to monitor numerous intracellular parameters such as pH and Ca(2+) concentration, but not all of them are equally suitable for this type of work. Genetically engineered fluorescent proteins can be used to visualise the fine dendritic structure of neurones or track particular intracellular structures and proteins. They have also been used to generate indicators for Ca(2+), cAMP and other molecules. While conventional chemical indicators can be either loaded into neurones via patch pipettes or as membrane-permeable esters, protein indicators can be expressed in various types of cells using adenoviral vectors. Adenoviral transgenesis can be performed in vitro in both acute slices and organotypic slice cultures. Organotypic slice cultures give excellent optical access to neurones loaded with either conventional fluorescent indicators or transfected with adenovirus to express fluorescent proteins. They are most suitable for experiments where both conventional and genetically engineered indicators are combined. Single photon imaging in brain slices is limited to the superficial layers (approximately<or=50 microm), while multiphoton excitation has a much greater depth of penetration. However, the overall optical resolution achievable in single photon mode is at least as good as when using multiphoton excitation.

Differential x-ray phase contrast imaging using a shearing interferometer

An x-ray interferometer has been developed that uses two transmission phase gratings to analyze wave front distortions in the hard x-ray range. The interferometer is insensitive to mechanical drift and vibrations, and it is tunable over a wide range of photon energies. This setup was used for differential phase contrast imaging of low-absorbing test objects. We obtained micrographs with moiré fringes of good visibility, which revealed the local phase shift gradient caused by the objects. A comparison with numerically simulated images indicates that quantitative analysis of unknown phase objects is possible.

Optical far-field microscopy of single molecules with 3.4 nm lateral resolution.

Optical far-field imaging of single molecules in a frozen solution at 1.2 K with a lateral resolution of 3.4 nm is reported. The mechanical stability of the fluorescence microscope, especially of the low-temperature insert, allows for the localization of fluorescing molecules with a reproducibility of better than 5 nm within observation times up to 10 min. For observation times of 9 h the reproducibility of the lateral position is limited to about 20 nm due to mechanical drift. Lateral position and orientation of 314 single molecules, present within the confocal detection volume of approximately 10 microm(3), are obtained. The possibility to correct for mechanical drift by monitoring the position of a spatial reference in the sample is demonstrated.

A two-channel four-dimensional image recording and viewing system with automatic drift correction.

Four-dimensional image acquisition systems have been described to analyse various developmental processes, for example, the Caenorhabditis elegans cell lineage. A practical problem that is often encountered during recordings is mechanical slippage of the microscope stage, causing the sample to drift out of focus. Furthermore, with the advent of green fluorescent protein (GFP) as an in vivo marker, affordable two-channel imaging systems are needed to correlate gene expression with changes through development. To overcome the mechanical drift a device-independent, software-only solution for the MacOS was devised that can compensate for Z-axis drifts in sample position. The software also allows recording of 4D stacks in two channels. To correct for drift, a small reference object beside the main object to be recorded is kept in focus using a simple autofocus principle, and this automatic drift correction allows for effective 4D recordings. In addition to the Z-axis drives and the shutters of the microscope, a video camera can be computer controlled to switch between two light levels. Second channel live GFP recordings are presently limited by the fact that the high intensity of the blue light heats and kills C. elegans embyros quickly. To view and annotate the stacks a MacOS viewing application was developed.

The effect of mechanical vibration and drift on the reconstruction of exit waves from a through focus series of HREM images

Experimental HREM images can show a limited resolution as a result of mechanical vibration and drift. In this paper the effect of such mechanical vibrations on the accuracy of the through focus exit wave reconstruction method is investigated for different thicknesses of a test structure of La 3Ni 2B 2N 3. A through-focus series of HREM images for this structure is simulated for different kinds of mechanical vibration corresponding to an information limit g of about 7 nm −1: (1) no mechanical vibration, (2) isotropic mechanical vibration, and (3) several anisotropic mechanical vibrations. From these through-focus series the reconstructed exit wave is calculated (Ultramicroscopy 64 (1996) 109). The above isotropic and anisotropic mechanical vibrations have a large effect on the reconstructed exit waves when compared with the reconstructed exit wave without mechanical vibration, i.e. the range of amplitudes and phases in a reconstructed exit wave decreases and the background intensity increases. The initial thickness and orientation can be obtained using a least-squares refinement procedure (Acta Crystallogr. A 54 (1998) 91) when there is no mechanical vibration present. In the case of isotropic or anisotropic vibration, the refined thickness and orientation are likely to give wrong results depending on the size of the vibrations and on the number of significant reflections (which is related to the size of the unit cell, the thickness and the misorientation).

Automated detection and tracking of individual and clustered cell surface low density lipoprotein receptor molecules

We have developed a technique to detect, recognize, and track each individual low density lipoprotein receptor (LDL-R) molecule and small receptor clusters on the surface of human skin fibroblasts. Molecular recognition and high precision (30 nm) simultaneous automatic tracking of all of the individual receptors in the cell surface population utilize quantitative time-lapse low light level digital video fluorescence microscopy analyzed by purpose-designed algorithms executed on an image processing work station. The LDL-Rs are labeled with the biologically active, fluorescent LDL derivative dil-LDL. Individual LDL-Rs and unresolved small clusters are identified by measuring the fluorescence power radiated by the sub-resolution fluorescent spots in the image; identification of single particles is ascertained by four independent techniques. An automated tracking routine was developed to track simultaneously, and without user intervention, a multitude of fluorescent particles through a sequence of hundreds of time-lapse image frames. The limitations on tracking precision were found to depend on the signal-to-noise ratio of the tracked particle image and mechanical drift of the microscope system. We describe the methods involved in (i) time-lapse acquisition of the low-light level images, (ii) simultaneous automated tracking of the fluorescent diffraction limited punctate images, (iii) localizing particles with high precision and limitations, and (iv) detecting and identifying single and clustered LDL-Rs. These methods are generally applicable and provide a powerful tool to visualize and measure dynamics and interactions of individual integral membrane proteins on living cell surfaces.

On the drift in stochastic mechanics

For a large class of Hamiltonians the author expresses the stochastic mechanical drift in terms of a solution of the classical equation of motion and comments on the use of Ito equations to study how quantum mechanics approximates classical mechanics.

Drive mechanism for a surface force apparatus

A technique is described for micropositioning a surface forces apparatus with low mechanical and thermal drift. The technique is less exacting and more stable than competing ones.