Tullio Tommasi

Computer-generated holograms of tilted planes by a spatial frequency approach

Computer-generated holograms of plane surfaces tilted and shifted with respect to the hologram plane are considered. The analysis is made in the spatial frequency domain by using the translation and rotation transformations of angular spectra. The frequency approach permits the use of the fast-Fourier-transform algorithm, which decreases the computation time and makes it possible to consider any position of the planes in space. Various configurations of tilted and shifted planes have been investigated, and computer-generated holograms of off-axis planes have been obtained. Computer and optical reconstructions, both of which show the feasibility of the proposed approach, have been carried out.

Frequency analysis of light diffraction between rotated planes

The relation for the angular spectra of rotated planes is evaluated, starting from the knowledge of the mono-chromatic scalar field on a given plane. Diffracted light on a tilted plane can then be calculated in the frequency domain by fast-Fourier-transform algorithms. Unlike the Fresnel and Fraunhofer approaches, this analysis does not require approximations; as a consequence, it permits any positions in space for the planes under investigation. Digital images are generated, which show the effects of rotation.

Interaction mechanism between electromagnetic fields and ion adsorption: endogenous forces and collision frequency

Abstract The adsorption of an ion messenger at a cell receptor is a potential target of electromagnetic exposure, which may affect the binding rate coefficient. The role of the endogenous field force experienced by an ion approaching the binding site is of paramount importance. In order to evaluate the effects of the exogenous field, the endogenous force obtained from the protein data bank has been approximated as a central field by means of a linear restoring force (“spring-like”) and by means of an inverse square field (“coulombic-like”). The first approximation is used in the classical Langevin-Lorentz model and the second in the quantum Zeeman-Stark model. The ion losses due to “collisions” near the binding site are modelled in the classical approach by a viscous collision frequency and in the quantum approach by a set of suitable inverse collision frequencies (lifetimes). In the case of collisions with solvent dipolar molecules (e.g. water), it is shown that the number of colliding solvent dipoles can be very small owing to the large gradients of the endogenous electric field. On the contrary, a binding site is, by definition, a spatial domain finite in size, where colliding molecules move in the Knudsen (ballistic) regime. As a consequence, the mean free path cannot exceed the domain dimension, irrespective of the low concentration of colliding molecules. It is concluded that the ion collision frequency (i.e. in classical terms, the effective viscosity of a binding site) can be many orders of magnitude lower than in the bulk solvent (lifetimes are longer in the quantum model), so that electromagnetic bioeffects may occur at low intensities of the exogenous fields.

3-D reconstruction in optical microscopy by a frequency-domain approach

Abstract A general and simple method for 3-D image restoration in optical sectioning microscopy is presented. A set of images taken with an optical system with a known 3-D point spread function (psf) are considered. The restoration task is described, pointing out theoretical constraints on recovering the actual spatial distribution of the original object. A spatial-frequency analysis is performed, using no a priori information about the specimens udner investigation. The feasibility and limitations of 3-D reconstructions are analyzed. Moreover, a procedure is proposed that allows one to recover object projections within an angle range strictly dependent on the psf of the system used. 3-D objects have been simulated in order to produce a set of images similar to those provided by an optical system. Restoration has then been accomplished, and results demonstrate that side-views of an object can be obtained to a satisfactory degree of accuracy. Finally, a discussion concerning the presence of transparent and opaque objects in the field of view is also presented.

Enhancement of the interaction between low-intensity R.F. e.m. fields and ligand binding due to cell basal metabolism

Power absorption by biological tissues, due to low‐intensity electromagnetic exposure at radio frequencies, as those generated by personal telecommunication systems, is typically negligible. Nevertheless, the electromagnetic field is able to affect biological processes, like the binding of a messenger ion to a cell membrane receptor, if some specific conditions occur. The depth of the attracting potential energy well of the binding site must be comparable with the radio frequency photon energy. The dependance of the binding potential energy on the spatial coordinates must be highly non‐linear. The ion–receptor system, in absence of the exogenous electromagnetic exposure, must be biased out of thermodynamic equilibrium by the cell basal metabolism. When the above conditions concur a low‐intensity radio frequency sinusoidal field is able to induce a steady change of the ion binding probability, which overcomes thermal noise. The model incorporates the effects of both thermal noise and basal metabolism, so that it offers a plausible biophysical basis for potential bioeffects of electromagnetic fields, e.g., those generated by mobile communication systems.

Experimental and theoretical surface acoustic wave analysis of thin‐film lipid multilayers

The leaky surface acoustic wave (LSAW) velocity of thin films of lipids on a glass substrate has been investigated, using a reflection acoustic microscope at a frequency of 1 GHz. Multilayers of ω‐tricosenoic acid (28–220 nm in depth), collected with the Langmuir–Blodgett technique have been deposited on silanized glass. V(z) curves have been measured, and the LSAW velocity has been calculated from them. The results point out that the velocity decreases linearly as the lipid‐layer thickness increases. A theory is also presented, which gives a linear dependence between the LSAW velocity and the layer thickness.

Influence of viscosity on the reflection coefficient at a fluid–solid interface

A viscous fluid can carry both an attenuated longitudinal wave and an attenuated shear wave. The presence of a shear wave makes it necessary to satisfy the boundary conditions for a solid–solid interface when calculating the reflection coefficient at a lossy‐liquid/solid interface. Numerical results are presented which point out the influence of viscosity on reflection coefficients.

Space-variant optical interconnection through the use of computer-generated holograms.

A space-variant optical interconnection through the use of computer-generated holograms is proposed, and specific configurations to increase the number of parallel channels are analyzed. To this end, the well-known method based on a matrix composed of subholograms is applied. The field diffracted by each channel (assumed to be square apertures) is calculated through the angular-spectrum technique, and the resulting fields are suitably superimposed to obtain a hologram matrix with a reduced bandwidth. Results show that a compact transmissive planar configuration can be handled; in particular, the small interconnect distance between the array planes and the hologram yields a limited system volume.

A frequency-domain analysis of 3D reconstruction techniques based on defocusing

A technique used for three-dimensional reconstruction of microscopic objects is based on linear processing of a collection of images taken at different focus positions, that is, acquired step by step while the objective moves along the microscope optical axis. As the relationship between the object I(x,y,z) and the collection of images (if these latter are enough) is known to be a convolution via the microscope point spread function, a deconvolution procedure yields I(x,y,z). Here I(x,y,z) is the local absorption of the object. Based on the fact that reasonable approximations for the point spread function are available in the literature, the above technique seems to work satisfactorily, and has been applied by various researchers. In the present work, the method is analyzed from a strictly mathematical point of view. It Is shown that being the optical transfer function (OTF), that is, the Fourier transform of the point spread function, identically vanishing in an infinite region of the frequency domain, a deconvolution procedure is not feasible. If the Z-coordinate refers to the optical axis, the OTF is actually zero outside a conical region in the frequency domain. It is also shown that what can be actually recovered are projections of the given object. To this end, the so-called slice theorem, or projection theorem, is used. More exactly, we prove that one can obtain all projections of the object within an angle of projection-with respect to the optical axis-not greater than the aperture angle of the image formation system, that is, the microscope. Examples of simulations and of processing of experimental images are reported.

Acoustical Microscopy Applications for Living Cells Investigations

Several authors 1,2,3 have shown that scanning reflection acoustic microscopy operating in the GHz range is a powerful tool for observing living cells adhering to a substrate in culture; the related procedure is somewhat similar to reflection contrast optical microscopy 4. Acoustic images contain information relevant to cell topography and cell attachment sites. Computer processing of digital acoustic images results in a great enhancement of these two features. Moreover, further information can be gained by comparing experimental data with those obtained by modelling and computer simulating the whole process of acoustic image formation. Such a model will be described in the next section. This description will be followed by specific examples of cell image processing and by comparisons between experimental and computer simulation results.