1,721,284 research outputs found
On the structural organization of macromolecules using chiral sensitive differential scattering of circularly polarized light
No full textDifferential scattering of circularly polarized light is demonstrated to characterize the macromolecular structures consisting of hierarchical chirality. We modeled the B-DNA structure composed of a double-helix and a base-pairs helical structure. The angle-resolved scattering of circularly polarized light calculated for the B-DNA shows the additive behavior of the scattering signal contributed by the two individual chirality levels of B-DNA structure, a double-helix and a base-pairs helix. This additive behavior of angle-resolved scattering signal has also been demonstrated for other macromolecular structures comprising different chirality levels; a biological cell is also mimicked as a nucleated sphere, a sphere with a helical nucleus in its core. The individual chiral features of a structure add up to the angle-resolved scattering signal of circularly polarized light produced by the parent structure. The total scattered intensity calculations are also demonstrated. These electromagnetic wave scattering calculations can offer a label-free approach to characterize chiral macromolecular structures at the nanoscale level
Erratum to: Optical nanoscopy (La Rivista del Nuovo Cimento, (2020), 43, 8, (385-455), 10.1007/s40766-020-00008-1)
No full textAfter publication of the article we noticed that equations number 24 and 25 missed a convolution sign
Printability conditions for an all-solid-state laser transfer
No full textSeveral laser technologies exist capable of adding solid materials to a targeted area of a substrate, including photopolymerization, laser sintering, or laser-induced forward transfer. However, the added material normally undergoes a phase change, causing adverse effects such as shrinkage, stress, or degradation. As recently demonstrated, this issue can be addressed by using laser pulses to mechanically delaminate and eject a disk from a solid film. In this case, the laser plays the role of a catapult, with minimal thermal damage to the transferred disk. Despite proven success in micro-electronics and micro-optics, little is known about the mechanical properties of the film that lead to a crack-free all-solid-state transfer. Here, we present a theoretical and experimental study on the effects that film rigidity, elasticity, and plasticity play on laser catapulting. By combining the thermodynamic equations of the laser-generated propulsion force with the theory of thin plate bending, we derived an analytical model that fully describes the list of events responsible for disk ejection. The model is in good agreement with experiments using elastomers, polymers, and metals. A complete printability map based on the film mechanical parameters is reported, which can help to broaden the family of materials suitable for laser additive manufacturing
Role of scattering and nonlinear effects in the illumination and the photobleaching distribution profiles
No full textNonlinear optical scanning microscopy has become a useful tool for living tissue imaging. Biological tissues are highly scattering media and this leads to an exponential attenuation of the excitation intensity as the light travels into the sample. While performing imaging of biological scattering tissues in nonlinear excitation regime, the localization of the maximum two-photon excitation (2PE) intensity was found to shift closer to the surface and the 2PE imaging depth limit appears strongly limited by near-surface fluorescence. In this work, we computed the illumination and the photobleaching distribution to characterize the effects induced by scattering. An experimental test has been carried out by imaging, with 0.9 NA objective, thick scattering fluorescent immobile sample (polyelectrolyte gel) as a phantom for biological samples. Results confirm that under these conditions no photobleaching effects due to scattering occur close to the surface
Circular intensity differential scattering of light to characterize the coronavirus particles
No full textAngle-resolved circularly polarized light scattering calculations are demonstrated to identify virus particles from nonvirus particles. A coronavirus particle is modeled as having a spherical shaped envelope with cylindrical spikes projected from the envelope surface, and the single-stranded ribonucleic acid (RNA) genome polymer has been mimicked with a toroidal helix. The influence of genome polymer packaged as a standard helix in the virion core is also demonstrated. We investigated four different electromagnetic models: (i) a nucleated sphere with spikes that is a coronavirus particle, (ii) a nucleated sphere with no spikes, (iii) a homogeneous sphere, and (iv) a respiratory fluid containing a virus particle. The angular pattern of scattered circularly polarized light, the circular intensity differential scattering of light (CIDS), served as a particle's signature. This scattering signature is found sensitive to the chiral parameters that reveal information about the particles. The effect of changes in the RNA polymer, changes in its packaging, number of turns, handedness, and size are demonstrated on the scattering calculations. Additionally, the extinction efficiency, the depolarization ratio, the total scattered intensity, and the effect of changes in the wavelength of incident light on these scattering quantities are investigated. This biophysical method can offer a label-free identification of virus particles and can help understand their interaction with light
Advanced correlative light/electron microscopy: current methods and new developments using Tokuyasu cryosections
No full textMicroscopy is an essential tool for analysis of cellular structures and function. With the advent of new fluorescent probes and super-resolution light microscopy techniques, the study of dynamic processes in living cells has been greatly facilitated. Fluorescence light microscopy provides analytical, quantitative, and three-dimensional (3D) data with emphasis on analysis of live cells using fluorescent markers. Sample preparation is easy and relatively inexpensive, and the use of appropriate tags provides the ability to track specific proteins of interest. Of course, only electron microscopy (EM) achieves the highest definition in terms of ultrastructure and protein labeling. To fill the gap between light microscopy and EM, correlative light and electron microscopy (CLEM) strategies have been developed. In particular, hybrid techniques based upon immuno-EM provide sensitive protein detection combined with high-resolution information on cell structures and protein localization. By adding the third dimension to EM with electron tomography (ET) combined with rapid freezing, CLEM techniques now provide additional tools for quantitative 3D analysis. Here, we overview the major methods applied and highlight the latest advances in the field of CLEM. We then focus on two selected techniques that use cryosections as substrate for combined biomolecular imaging. Finally, we provide a perspective of future developments in the field
Materiale composito comprendente allumina porosa anodica ed una matrice polimerica, e suo uso per il restauro dentale
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