Abstract: A method of effecting delayed release of a fluid (19) comprises providing the fluid in a vessel (12) having a discharge aperture (14) provided with a polymeric barrier (5) to fluid release. The barrier (15) is caused to degrade to provide for failure of the barrier and discharge of the fluid. The liquid to be discharged may be an aqueous medium and the barrier (15) may be of a polymeric material capable of forming in the presence of the aqueous medium a gel that will dissolve therein so as to cause failure of the barrier. The polymeric material may be a cellulose ether. The fluid may, for example, comprise a culture of microorganisms which are subjected to pre-enrichment in the vessel for a predetermined period of time prior to failure of the barrier (15) and discharge of the culture into, for example, a selective medium.

Abstract: A timing circuit records the duration of intervals between a plurality of events in a data stream. The circuit includes at least two timing channels, each arranged to generate a signal representing time elapsed between events. The rate of change of the signal generated by each timing channel varies with increasing interval duration, and the timing channels are arranged such that each event terminates the operation of one timing channel and initiates operation of another timing channel.

Abstract: Analytical apparatus includes a pyroelectric or other thermo-electric transducer element (10) in strip form. Thin film electrodes (12,14) are provided and one or more dots of reagent (16) are deposited on the transducer surface. A small amount of biological or other sample is deposited over the reagent dots which undergo selective colorimetric changes. The transducer is illuminated from below by LED light sources (24) and light absorption in the reagent regions is detected as microscopic heating at the transducer surface. The electrical signal output from the pyroelectric transducer is processed to derive analyte information.

Abstract: In a method and apparatus for examining samples comprising individual objects (28) of macromolecular or similar size, or smaller, an instrument element (14) comprises a substrate (16) overlaid with a thin film layer (18) of a material that is electrically conductive and/or at last partly optically opaque. A discontinuity comprising an aperture (26) or an asperity is formed in or on the element (14) in a known location, and the sample (28) is brought to this discontinuity so that it is not necessary to search for the sample by scanning. Energy (e.g. electrical energy or light) is applied to the element (14) and, with the latter and the sample in intimate association, e.g. with the sample inside the aperture (26), changes in the radiation from the sample site resulting from the presence of the sample are detected.

Abstract: A transponder includes a receiver for receiving a radio interrogation signal. The transponder also includes a phase locked loop decoder for deriving a reference signal from the received interrogation signal, and a radio transmitter for transmitting a transponder reply signal. The phase locked loop has an output which feeds the AC reference signal to the transmitter. The transmitter includes a frequency doubler which generates a transmitter radio frequency at double the frequency of the reference signal. The transmitter radio frequency is therefore controlled by the radio frequency of the interrogation signal. The phase locked loop includes a divide-by-N counter, where N is a predetermined integer parameter. The parameter N determines the derivation of the reference signal frequency from the interrogation signal frequency.

Abstract: The concentration of an ionic species (e.g. K.sup.+) is determined using an ion sensitive electrode having an appropriate membrane (e.g. valinomycin in plasticised PVC). In place of a conventional reference electrode, the half cell is completed with an electrode having an identical membrane but lacking the constituent producing the ion-selective response (e.g. plasticised PVC). The working and reference electrodes can then be made in substantially the same manner to null of interferents. The difficulties associated with double junctions are avoided.

Abstract: An electrical measuring device utilizing a shunt, an electronic measuring circuit floating at the potential of the shunt and a first voltage divider connected between the shunt and a neutral point to provide a first voltage signal to the circuit. To obtain the benefit of decoupling the potential between the shunt and the intermediate point of the first voltage divider, the device includes an additional terminal connected to the shunt by a second voltage divider, whose intermediate point supplies a second voltage signal used differentially with the first.

Abstract: Particle velocity is determined optically through the use of crossed interference fringe patterns. The fringe patterns are produced by passing laser beams of distinct wavelength along a common optical fibre and through two crossed diffraction gratings which are bonded to the free end of the fibre. Each diffraction grating is constructed in the manner of an interference filter so as to produce interference fringes at one wavelength but to transmit the other wavelength substantially uniformly across the grating. Other interference elements can be used in place of diffraction gratings and the use of a single diffraction grating is envisaged in certain circumstances. An indication of the sense of particle movement can be achieved by creating a fringe pattern of steadily increasing fringe spacing.

Abstract: Separate pulse inputs from respective metering circuits, representing the reactive R and in-phase W power components, are converted to a pulse output V representing the vector sum of those components. The two inputs are applied to increment respective registers, the output V is held in a third register, and a fourth register is provided to store the REMAINDER value (W.sup.2 +R.sup.2)-(V+1).sup.2. The meter includes a processor for incrementing the REMAINDER value by 2W+1 for each increment of W and 2R+1 for each increment of R and for incrementing V whenever the REMAINDER value is zero or positive and at the same time reducing the REMAINDER value by 2V.sub.1 +1, where V.sub.1 is the incremented value of V. The FRACTIONAL error in the value of V is determined by means of a look-up table.

Abstract: An electrochemical reference element is proposed having a metal electrode such as silver coated with the tetraphenyl (TPB) salt of the metal. The element may form the internal reference of an ion selective electrode with an ion selective membrane carried directly upon the TPB coating. The element provides a thermodynamically reversible couple suitable for use in a non-aqueous environment.

Abstract: Apparatus for optical analysis of particles such as biological cells utilizes twin beams passing through a common optical fibre to avoid problems of alignment. For scattering measurements, a narrower beam can be used to gate detection of a broader beam to avoid amiguities associated with off-axis particles. The twin beams can also be used for thermal lensing, fluorescence or other techniques. Different beam diameters can alternatively be achieved in a single beam by controlling the focal length of a beam focussing lens.

Abstract: A filter which is particularly useful with biological material is formed of porous piezoelectric material such as PZT or Polyvinylidene fluoride. By an application of a voltage to the piezoelectric material, the filter body is caused to vibrate so as to inhibit fouling. In a modification, the piezoelectric material is not itself porous but is bonded to a filter membrane such that vibrations of the piezoelectric material are transmitted to the membrane. Through suitable control of the vibration, the selectivity of the filter can be controlled. In other modifications the vibratory movement of the filter membrane can be produced in other ways such as electro-mechanically.

Abstract: A method of investigating the condition of biological particles, in particular the fraction of viable cells in a bacteria population involves applying a voltage and monitoring the voltage induced by magnetic induction in a detector coil. The applied voltage is of a variable frequency alternating voltage and is preferably induced in the medium through a drive coil.

Abstract: Apparatus for determining the amount of biological material in a fluid medium, typically the concentration of bacteria in a fermentation chamber, has a test cell through which a medium can be passed with bacteria or after bacteria have been removed by filtration. In the test cell a vibratory element is excited to a resonant frequency indicative of density and a comparison of medium density and medium plus bacteria density reveals the bacteria concentration.

Abstract: A method of investigating the condition of biological particles, in particular the fraction of viable cells in a bacteria population involves applying a voltage and monitoring the voltage induced by magnetic induction in a detector coil. The applied voltage is of a variable frequency alternating voltage and is preferably induced in the medium through a drive coil.