Showing papers by "David A. Jackson published in 1988"

Visualization of a filamentous nucleoskeleton with a 23 nm axial repeat.

Abstract: Whether nucleoskeletons seen after extracting cells are preparative artefacts is controversial Using an extraction method that preserves vital nuclear functions, we have visualized part of a nucleoskeleton by electron microscopy of thick resinless sections Cells encapsulated in agarose microbeads are lysed using Triton in a physiological buffer; the agarose coat prevents aggregation and protects fragile cell contents These extracted cells are accessible to small molecules and transcribe and replicate at rates close to those in vivo After electroeluting most chromatin after treatment with HaeIII, a skeleton is uncovered which ramifies throughout the nucleus Individual filaments are approximately 10 nm wide with an axial repeat of 23 nm, characteristic of intermediate filaments

A gentle method for preparing cyto- and nucleo-skeletons and associated chromatin.

Abstract: We describe a method for permeabilizing and extracting cells that preserves both structure and function whilst allowing the cell derivatives to be handled freely. Cells are encapsulated in microbeads of agarose; the coat of agarose, which is freely permeable to small molecules, forms a protective layer around fragile cell constituents. Cells are then permeabilized by the non-ionic detergent Triton X-100 or antibody and complement in a buffer whose ionic composition mimics that of the cytoplasm. The resulting structures have been characterized morphologically (by immunofluorescence and electron microscopy) and biochemically. Lysis with Triton removes both cell and nuclear membranes, and extracts most of the cytoplasm to leave chromatin surrounded by cytoskeleton; nucleus and cytoplasm then become accessible to triphosphates, enzymes and antibodies. Lysis with complement permeabilizes the cell membrane but leaves the nuclear membrane intact; triphosphates and restriction enzymes, but not antibodies, can then enter both nucleus and cytoplasm. Both types of lysis yield preparations whose chromatin template remains essentially intact, and which is replicated and transcribed at rates close to, or greater than, those found in vivo. Treatment of complement-lysed cells with Triton reduces the very efficient DNA synthesis, implying that the nuclear membrane is involved, directly or indirectly, in replication.

Fibre-optic interferometric sensor utilising low coherence length source: resolution enhancement

Abstract: A fibre-optic interferometric sensor is described based on a low-coherence source. A novel form of homodyne signal processing is used in which the interferometer is locked to the quadrature point nearest to maximum visibility. This technique avoids the ambiguities which arise from the use of a high-coherence source in interferometers, where the transfer function is periodic.

Two-dimensional fibre-optic laser velocimetry using polarisation state control

Abstract: A two-dimensional fibre-based laser Doppler velocimeter has been constructed where the orthogonal velocity distributions can be recovered either sequentially or simultaneously using a novel fibre-optic polarisation state control scheme. The scheme is described and the benefits of the two approaches are discussed. The instrument is demonstrated in a simple fluid flow experiment.

Time-division multiplexing of fibre optic interferometric sensors using a frequency modulated laser diode

Abstract: A multiplexed sensing system based on a frequency modulated laser diode is demonstrated, where a time addressing technique is used to identify signals from different interferometers. It is shown that sensor interferometers with the same path differences can be deployed in the system and crosstalk between different interferometers is avoidable.

Extended-range interferometry using a coherence-tuned, synthesised dual-wavelength technique with multimode fibre links

Abstract: We describe in the letter a technique for making extended-range interferometric measurements with a coherence multiplexed system by means of a variation on the dual-wavelength technique. The interferometer is illuminated with a single source and the two wavelengths are synthesised at the output by means of an interference filter.

A fibre-optic frequency shifter utilizing travelling flexure waves in birefringent fibre

Abstract: A fibre-optic frequency shifter based on the use of flexure waves to produce a travelling perturbation which couples the polarization modes of birefringent optical fibre is described. In experiments, frequency shifts of about 790 kHz were produced. A dispersion relation for the flexure waves in the fibre has been derived and was shown to be valid in experiments. The device is described using coupled mode theory, and it is shown that optimum mode coupling will occur when the wavelength of the flexure waves is twice the birefringent beat length of the fibre.

All-fiber-optic polarization state azimuth control: application to Faraday rotation

Abstract: An all fiber-optic system for the control and modulation of the azimuth of a linearly polarized beam is described. The experimental configuration is basically that of a Mach-Zehnder interferometer but with the birefringence of the two fiber arms controlled to produce orthogonal circular states of polarization which recombine in the final directional coupler. Azimuth control is then achieved by relative phase modulation using a piezo-electric element. The system has required the use of monomode fiber directional couplers of accurately characterized polarization properties, and the development of fiber linear retarders. The application of the system in the measurement of electric currents via Faraday rotation is described, although extensions to other types of optical instrument are equally feasible. >

Multiplexed fibre-optic interferometric sensing system: combined frequency and time division

Abstract: It is shown that a frequency modulated laser diode source can be used to combine frequency division multiplexing and time domain addressing techniques to increase the number of interferometric sensors in a multiplexed fibre optic system. Demultiplexing is carried out in both the frequency and time domains to generate independent heterodyne carriers for different interferometers.

Fibre-optic transit velocimetry using laser diode sources

Abstract: A simple fibre-based transit anemometer has been constructed using laser diode sources. A pair of single-mode optical fibres is used to facilitate the production of the input waists for the beamforming system directly and so reduce the required number of optical components. Extension to a two-dimensional transverse system is straightforward.

Frequency-locked diode laser for interferometric sensing systems

Abstract: Interferometric sensors for slowly varying measurands, such as temperature or pressure, require a long term frequency stability of the source. We describe a system for frequency locking a laser diode to an atomic transition in a hollow cathode lamp using the optogalvanic effect.

Interferometric chromatic dispersion measurements on short lengths of monomide optical fiber

Abstract: Chromatic dispersion in an optical fiber is the limiting factor in achieving very high-bandwidth communications systems. Several techniques are available for measuring dispersion; for a review see Ref. 1. However, only interferometric techniques have the ability to obtain a resolution of >1 ps km−1 nm−1 for short, ~ 1-m, lengths of fibers. The ability to make dispersion measurements in short lengths of fiber is very important since it enables economic storage of fibers to test for any effects associated with aging, determination of the quality of the draw perform, and testing of short lengths of new or experimental fibers.

Monomode fiber modulators: Frequency and polarization state control

Abstract: Two experimental fiber components are described that exploit the properties of highly birefringent monomode optical fiber. In the first the generation of a traveling ultrasonic flexure wave on the fiber produces a frequency shift on the input optical signal. In the second a variable axial tension modulates the differential phase retardance between the two guided polarization eigenmodes to produce an arbitrary output polarization state from a linear input state (or vice versa) without loss of optical power.

Control: Application to Faraday Rotation

Abstract: An all-fiber-optic system for the control and modulation of the azimuth of a linearly polarized beam is described. The experi- mental configuration is basically that of a Mach-Zehnder interfer- ometer but with the birefringence of the two fiber arms controlled to produce orthogonal circular states of polarization which recombine in the final directional coupler. Azimuth control is then achieved by rel- ative phase modulation using a piezo-electric element. The system has required the use of monomode fiber directional couplers of accurately characterized polarization properties, and the development of fiber lin- ear retarders. The application of the system in the measurement of electric currents via Faraday rotation is described, although extensions to other types of optical instrument are equally feasible. I. INTRODUCTION ECENTLY we have reported fiber-optic techniques R for producing a linearly polarized optical beam of controllable azimuth ( 13. These systems ofler consider- able advantages over conventional ones in terms of size, cost, and compatability with fiber-optic probes for remote measurements. However, the system described previ- ously were hybrid in that only limited use was made of fiber optics, and many conventional components, includ- ing wave plates and beamsplitters, were also required. We have therefore developed new techniques which allow the replacement of all the previously used conventional com- ponents to realize an all-fiber system, with consequent substantial advantages of mechanical stability and mini- aturization. As we have described previously (l), (2) polarization azimuth control and measurement forms the basis of a range of optical instrumentation and experimental tech- niques. Examples include ellipsometry, polarimetry and a wide range of light scattering experiments. To illustrate the potential of the present system, we have applied it to the measurement of electric current via Faraday rotation produced in the fiber guided beam. However. the signal processing schemes are equally applicable to the mea- surement of other circular birefringence phenomena, for example, optical activity. 11. TtwoRY

High Speed Thermometry Utilising Multiplexed Fibre Fabry-Perot Interferometers

Abstract: The results of an investigation into the temporal response of fibre optic interfero-meters to heat pulses is presented. A rise time of -4 s was determined where an electric arc was used to heat the fibre cladding. A response time of < 10-4 s was observed when an optical technique was used to directly heat the fibre core. These measurements were performed with a new remote optical configuration which could be used as a miniaturised sensing element. The feasibility of multiple measurement with this new fibre Fabry-Perot interferometer was studied, and two multiplexed sensing systems based on frequency division and coherence multiplexing are described.

Laser Diode Frequency Stabilisation Techniques For Interferometric Sensors

Abstract: High accuracy interferometric systems sensing slowly varying measurands place great demands on the frequency stability of the optical source used. In this paper, we determine the stability requirements of interferometric systems employing various signal processing techniques, and describe investigations into methods for locking the laser diode to a unique frequency by means of a monochromator, a diffraction grating, an interference filter and an atomic transition in a hollow cathode lamp.