Development of latent fingerprints using a corona discharge.

A novel technique for the development of latent fingerprints is presented. It is based on placing a fingerprint-bearing object inside a corona discharge induced plasma. The development of various real and artificial fingerprints on metallic substrates under a wide range of conditions is studied. Using the results of the development experiments and the results of X-ray photoelectron spectroscopy, it is shown that the development is based on oxidation of the fingerprint background. This is achieved by strong oxidizers generated by the discharge process, while saturated fatty-acids found in sebaceous fingerprints protect the area beneath them, resulting in a visible fingerprint. The process is optimized by minimizing the electrode gap distance and maximizing the peak discharge voltage and the pulse repetition frequency.

Interferometric technique for measuring the refractive index variation of a liquid with temperature.

A technique for measuring the variation of refractive index of a liquid as a function of temperature or solute concentration using a Mach-Zender interferometer is described. The principal difficulty of obtaining a uniform temperature along the optical path in the sample liquid while simultaneously varying the temperature at a reasonable rate is overcome by heating the liquid in a separate vessel and injecting the heated fluid into the test vessel as a series of jets to encourage turbulent mixing. An equivalent resolution in the refractive index variation of 2x10(-6) was obtained. The above method was used to determine the variation of refractive index in a 0.1% NaCl/H(2)O solution in the temperature range 23 degrees -33 degrees C.

Interferometric measurement technique for the temperature field of axisymmetric buoyant phenomena.

A method is described to measure the temperature field of axisymmetric laminar thermals, plumes, and starting plume caps in a liquid. The sample liquid is placed in a Mach-Zender interferometer, and an infinite-fringe interferogram is recorded on photographic film. By comparison with a bar pattern interferogram, the fringe shift field was measured to an accuracy of +/-0.02. The Bockasten series approximation of the Abel transformation was applied to the fringe shift field to obtain the radial refractive index variation field, which in turn could be related to the temperature variation field through an empirical relationship. Temperature accuracies in the range of +/-0.05 to +/-0.5 degrees C were obtained. The radial temperature profile of the plume was found to be monotonically decreasing, while the cap had a local maximum offset from the axis.

Scanning technique for obtaining linear fringe shift readout from a high resolution interferometer.

A technique is described for obtaining a linear readout of fringe shift from a high resolution Fabry-Perot interferometer. One mirror of the interferometer is mounted on a piezoelectric crystal driven by a high frequency sinusoidal voltage. A signal proportional to the mirror displacement is displayed on the Y axis of an oscilloscope, while the X axis is swept with time. Each time the interferometer passes through a transmission maximum, a pulse is produced which is fed to the Z axis of the oscilloscope, producing an intensified dot. The displacement of the resultant row of dots from its ambient position is linearly proportional to the fringe shift occurring within the interferometer, has no sign of ambiguity, and is independent of the finesse. All the circuits required for producing the readout were realized using the internal circuitry of a standard laboratory oscilloscope.