An optical self-calibrating technique for the dynamiccharacterization of PZT's

A system suitable for the measurement of linear sinusoidal vibration amplitudes is described. The signal beam of a Michelson interferometer is focused on the vibrating target while a suitable phase noise is applied to the reference arm of the interferometer. Signal processing is based on the null adjustment of the Bessel coefficients J₁ and J₂ derived from the signal provided by a single photodiode placed in the center fringe of the interference pattern. The system has been shown to be self-calibrating and intrinsically immune to mechanical perturbations induced in the interferometer. The technique proposed has been experimentally demonstrated by measuring the vibration amplitude of a PZT device in the amplitude range from 0.4 to 1.7 μm and in the frequency range from 8 to 22 kHz     

Three-dimensional optical measurements and reverse engineering for automotive applications

The paper describes a very special and suggestive example of optical three-dimensional (3D) acquisition, reverse engineering and rapid prototyping of a historic automobile, a Ferrari 250 Mille Miglia, performed primarily using an optical 3D whole-field digitiser based on the projection of incoherent light (OPL-3D, developed in our laboratory). The entire process consists in the acquisition, the point cloud alignment, the triangle model definition, the NURBS creation, the production of the STL file, and finally the generation of a scaled replica of the car.The process, apart from the importance of the application to a unique, prestigious historic racing car, demonstrates the ease of application of the optical system to the gauging and the reverse engineering of large surfaces, as automobile body press parts and full-size clays, with high accuracy and reduced processing time, for design and restyling applications.     

In-field performance of an optical digitizer for the reverse engineering of free-form surfaces

The use of OPL-3D, a robust, flexible and easy-to-use optical digitizer, in conjunction with reverse engineering procedures is presented. The optical digitizer is used as a stand-alone (i.e., not in tandem with popular CMM’s) system, whose output point clouds can be manipulated, by means of both specifically-designed software and high-performance commercial software, to produce mesh surfaces and NURBS of the acquired shape. The digitizer-process combination yields accurate digital replicas of the target object, the accuracy of the whole combination being on the order of 1/1500 of the measurement range. The speed of acquisition, combined with the above high accuracy, the ease of use and the fact that recalibration is seldom required makes the digitizer ideal for reverse engineering in an enormous number of applications ranging from automotive to biomedical.     

Refractive hazards of intraoperative retinal photocoagulation

Coaggregations between bacterial species have been widely studied in vitro but not in the mouth. A new in vivo assay was used to measure the rate and composition of indigenous plaque formation onto bovine enamel chips covered with a continuous layer of bacteria. Chips were covered with Streptococcus oralis ATCC 10557, which coaggregated with many oral species, or Streptococcus gordonii S7, which did not coaggregate with these oral species, and placed in the mouth for 4 and 24 h. There were no differences in the number of most indigenous bacterial species isolated from the two streptococcal surfaces. However, the number of Actinomyces viscosus as a proportion of total Actinomyces spp. was significantly different on the two surfaces at 24 h. With the exception of Actinomyces naeslundii and A. viscosus removed from the S7 surface, all indigenous species increased significantly in number from 4 to 24 h, irrespective of the streptococcal surface. This study demonstrated that interbacterial coaggregation had only a limited effect on in vivo plaque development. Thus suggesting that environmental factors, growth or other adherence phenomena are dominant in in vivo plaque formation.     

A simple and reliable system for measuring the refractive index ofliquids using a position-sensitive detector

A simple and yet efficient apparatus for the measurement of the refractive index of liquids has been developed, with the purpose of controlling adulteration in liquids of everyday use. In the system, the index of refraction of the liquid under test is determined by measuring the lateral displacement of a laser beam, that passes obliquely through a rectangular cell filled with the liquid under characterization. The lateral displacement is accurately determined by a position-sensitive detector. A careful analysis of the errors that can be obtained with the system has been carried out, that yielded calibration curves for easy on-line correction. To characterize the performance of the system, a series of tests has been performed on simple liquids, under controlled conditions. The residual errors have proven to be within one part over 10³. The proposed system is suitable for easy automation, obtaining simple and accurate measurements that can be performed also for volatile compounds     

An automatic pulsed laser microfluorometer with high spatial and temporal resolution

The paper describes an automatic pulsed laser microfluorometer with high spatial and temporal resolution, developed in our laboratories. The instrument consists of: (i) a nitrogen-laser-pumped dye-laser for the excitation of the fluorescence, (ii) a microscope with additional optics to focus the excitation beam on the sample and to collect the fluorescence, (iii) filters or monochromators to select the output wavelength, (iv) a fast photomultiplier tube to detect the signal, and (v) a dual time-scale microprocessor-controlled signal averager for the acquisition and processing of the signal. Examples are given that show the potential of the time-resolved fluorescence microscopy in studying, quantitatively and qualitatively, the properties of fluorescent molecules.     

Light-induced transmission changes in liquid crystal displays foradaptive pattern projection

The changes in the transmission and contrast properties of a super-twisted nematic liquid crystal display panel, induced by the light impinging on the panel itself, have been studied. Upon illumination by laser radiation with power density close to that used in practice, the transmittance of the panel increases or decreases according to the brightness voltage that sets the transmittance level. The dynamics of the transmittance change are typically bi-exponential, with a shorter decay time on the order of a fraction of a second and a longer decay on the order of tens of seconds. The observed changes were interpreted and modeled by considering local temperature changes in the crystal because of the light impinging on it. The temperature changes produce a shift of the transmittance curve and a change of slope in its central region. The presence of the dip after the Frederickzs region accounts for the anomalous behavior of the transmittance in that portion of brightness voltages     

Online dimensional analysis of surfaces using optical filtering andelaboration techniques in the Fourier plane

A simple and efficient method for online dimensional analysis and quality control of one-dimensional and two-dimensional objects is presented. It is based on optical image elaboration using filtering techniques in the Fourier plane. The Fourier spectrum of the light transmitted through the object is filtered by suitable means to eliminate unwanted spatial components. Inverse transformation of the spectrum provides the filtered light distribution to the detector. The method makes it possible to enhance greatly the signal-to-background ratio both in the case of a uniform light background and in the case of undesired spatial components in the image light distribution. It provides a quasi-digital presentation of the object profile directly to the detector without any need for time-consuming computer elaborations. A preliminary implementation of the system is described, both for one-dimensional and two-dimensional objects, and experimental results are presented     

Vitreous laser absorption following fluorescein angiography in diabetic patients

Spinal manipulation is commonly used by some therapists for the treatment of cervical pain. Flexion-extension of the cervical spine produces sliding movements of one vertebra over the one below it, which leads to physiological reduction in the antero-posterior diameter of the spinal canal. Spinal manipulation provokes movements that exceed the physiological limits of these articulations and thereby lead to a more significant reduction of the canal diameter. In patients with pre-existing stenosis of the canal or those with vertebral instability, these movements may cause (or aggravate) myelopathy. For this reason, a thorough neurological examination and cervical spine films should be considered mandatory in patients being considered for spinal manipulation. This report describes four patients with cervical myelopathy and/or radiculopathy caused or aggravated by spinal manipulation. In one patient, magnetic resonance scans before and after chiropractic treatment strongly suggests that the disc prolapse syndrome experienced by the patient was provoked by the spinal manipulation.