The new generation of SPAD—Single-Photon Avalanche Diodes arrays

In the last years the single-photon detection with silicon devices has become an important goal. Here we present the performance of a new generation of single-photon avalanche diodes manufactured by ST-Microelectronics. The 5 × 5 array configuration has been also realized and the performances, in terms of crosstalk and common readout mode, have been investigated

Exploiting the tunability of stimulated emission depletion microscopy for super-resolution imaging of nuclear structures

Imaging of nuclear structures within intact eukaryotic nuclei is imperative to understand the effect of chromatin folding on genome function. Recent developments of super-resolution fluorescence microscopy techniques combine high specificity, sensitivity, and less-invasive sample preparation procedures with the sub-diffraction spatial resolution required to image chromatin at the nanoscale. Here, we present a method to enhance the spatial resolution of a stimulated-emission depletion (STED) microscope based only on the modulation of the STED intensity during the acquisition of a STED image. This modulation induces spatially encoded variations of the fluorescence emission that can be visualized in the phasor plot and used to improve and quantify the effective spatial resolution of the STED image. We show that the method can be used to remove direct excitation by the STED beam and perform dual color imaging. We apply this method to the visualization of transcription and replication foci within intact nuclei of eukaryotic cells

Projected Quasi-particle Perturbation theory

The BCS and/or HFB theories are extended by treating the effect of four quasi-particle states perturbatively. The approach is tested on the pairing hamiltonian, showing that it combines the advantage of standard perturbation theory valid at low pairing strength and of non-perturbative approaches breaking particle number valid at higher pairing strength. Including the restoration of particle number, further improves the description of pairing correlation. In the presented test, the agreement between the exact solution and the combined perturbative + projection is almost perfect. The proposed method scales friendly when the number of particles increases and provides a simple alternative to other more complicated approaches

Fusion and Binary-Decay Mechanisms in the 35^{35}Cl+24^{24}Mg System at E/A ≈\approx 8 MeV/Nucleon

Compound-nucleus fusion and binary-reaction mechanisms have been investigated for the $^{35}$Cl+$^{24}$Mg system at an incident beam energy of E$_{Lab}$= 282 MeV. Charge distributions, inclusive energy spectra, and angular distributions have been obtained for the evaporation residues and the binary fragments. Angle-integrated cross sections have been determined for evaporation residues from both the complete and incomplete fusion mechanisms. Energy spectra for binary fragment channels near to the entrance-channel mass partition are characterized by an inelastic contribution that is in addition to a fully energy damped component. The fully damped component which is observed in all the binary mass channels can be associated with decay times that are comparable to, or longer than the rotation period. The observed mass-dependent cross sections for the fully damped component are well reproduced by the fission transition-state model, suggesting a fusion followed by fission origin. The present data cannot, however, rule out the possibility that a long-lived orbiting mechanism accounts for part or all of this yield.Comment: 41 pages standard REVTeX file, 14 Figures available upon request -

New insights in Progerin-induced modifications of chromatin landscapes

Genome structure, expression, and regulation are crucial in maintaining the physiological state of any cell. However, even a single variation in one of these processes can induce genomic instability, leading to different pathologies, including aging and cancer. Our work focuses on a particular model for of laminopathies disease, Hutchinson Gilford Progeria Syndrome, HGPS. HGPS is a genetic disorder in which patients show aging-related symptoms in the first years of their lives. HPGS is caused by a mutation in the Lamin A gene, LMNA, that causes the permanent anchoring of the mutated protein, named Progerin, to the nuclear membrane. This permanent bond causes abnormal tractions leading to a crumpled nuclear morphology that affects chromatin organization, inducing alteration in replication, transcription, and DNA repair. Indeed, one single point mutation in the LMNA gene results in massive damage to many cellular processes. Here, we exploit Structured Illumination microscopy, SIM, to investigate altered heterochromatin distribution in HGPS-model and compare the results with the control cell line. In particular, we explore how Progerin affects facultative heterochromatin organization in the proximity of the Nuclear Pore Complex, NUP, at the nuclear lamina level. To this aim, we perform multicolor SIM of DNA, Progerin or lamin (respectively HGPS or control), facultative heterochromatin (tagging histone H3K9me2) and NUP. Then, we combine SIM with Image Cross-Correlation Spectroscopy analysis, ICCS, to evaluate the differences in distances between NUP and H3K9me2. Our approach enables the visualization of Progerin-induced alterations of chromatin nanoscale organization at the single-cell level and will hopefully lead to a deeper understanding of the molecular mechanisms associated with HGPS development

Laser-ultraviolet-A induced ultra weak photon emission in human skin cells: A biophotonic comparison between keratinocytes and fibroblasts.

Photons participate in many atomic and molecular interactions and processes. Recent biophysical research has discovered an ultraweak radiation in biological tissues. It is now recognized that plants, animal and human cells emit this very weak biophotonic emission which can be readily measured with a sensitive photomultiplier system. UVA laser induced biophotonic emission of cultured cells was used in this report with the intention to detect biophysical changes between young and adult fibroblasts as well as between fibroblasts and keratinocytes. With suspension densities ranging from 1-8 x 106 cells/ml, it was evident that an increase of the UVA-laser-light induced photon emission intensity could be observed in young as well as adult fibroblastic cells. By the use of this method to determine ultraweak light emission, photons in cell suspensions in low volumes (100 microl) could be detected, in contrast to previous procedures using quantities up to 10 ml. Moreover, the analysis has been further refined by turning off the photomultiplier system electronically during irradiation leading to the first measurements of induced light emission in the cells after less than 10 micros instead of more than 100 milliseconds. These significant changes lead to an improvement factor up to 106 in comparison to classical detection procedures. In addition, different skin cells as fibroblasts and keratinocytes stemming from the same donor were measured using this new highly sensitive method in order to find new biophysical insight of light pathways. This is important in view to develop new strategies in biophotonics especially for use in alternative therapies