Time-resolved photoelectron and photoion fragmentation spectroscopy study of 9-methyladenine and its hydrates: a contribution to the understanding of the ultrafast radiationless decay of excited DNA bases.

The excited state dynamics of the purine base 9-methyladenine (9Me-Ade) has been investigated by time- and energy-resolved photoelectron imaging spectroscopy and mass-selected ion spectroscopy, in both vacuum and water-cluster environments. The specific probe processes used, namely a careful monitoring of time-resolved photoelectron energy distributions and of photoion fragmentation, together with the excellent temporal resolution achieved, enable us to derive additional information on the nature of the excited states (pp*, np*, ps*, triplet) involved in the electronic relaxation of adenine. The two-step pathway we propose to account for the double exponential decay observed agrees well with recent theoretical calculations. The near-UV photophysics of 9Me-Ade is dominated by the direct excitation of the pp* (1Lb) state (lifetime of 100 fs), followed by internal conversion to the np* state (lifetime in the ps range) via conical intersection. No evidence for the involvement of a ps* or a triplet state was found. 9Me- Ade–(H2O)n clusters have been studied, focusing on the fragmentation of these species after the probe process. A careful analysis of the fragments allowed us to provide evidence for a double exponential decay profile for the hydrates. The very weak second component observed, however, led us to conclude that the photophysics were very different compared with the isolated base, assigned to a competition between (i) a direct one-step decay of the initially excited state (pp* La and/or Lb, stabilised by hydration) to the ground state and (ii) a modified two-step decay scheme, qualitatively comparable to that occurring in the isolated molecule

An Experimental Platform for the Analysis of Polydisperse Systems Based on Light Scattering and Image Processing

In this work an experimental platform for light scattering analysis has been developed using image sensors, as CCD or CMOS. The main aim of this activity is the investigation of the feasibility of using these types of sensors for polydisperse systems analysis. The second purpose is the implementation of an experimental platform which is enough versatile to permit the observation of different phenomena in order to develop novel sensors/approach using data fusion

Development of a Novel Snom Probe for in Liquid Biological Samples

This work is focused on the study and implementation of a novel method for the development of probes for Scanning Near-field Optical Microscopy (SNOM). The proposed approach is based on the mechanical impedance matching between the optical fiber tip and the resonating tuning fork. This methodology allowed an increase of the quality factor of the piezoelectric resonator used as atomic force transducer in the SNOM probe, thus increasing its overall sensitivity. This kind of probes are often used on biological soft samples in liquid. The presence of water medium has a strong dumping effect on probe sensitivity. Experimental validation of the proposed methodology showed an increase of robustness of SNOM probes also for in liquid samples

Formation and destruction of polycyclic aromatic hydrocarbon clusters in the interstellar medium

The competition between the formation and destruction of coronene clusters under interstellar conditions is investigated theoretically. The unimolecular nucleation of neutral clusters is simulated with an atomic model combining an explicit classical force field and a quantum tight-binding approach. Evaporation rates are calculated in the framework of the phase space theory and are inserted in an infrared emission model and compared with the growth rate constants. It is found that, in interstellar conditions, most collisions lead to cluster growth. The time evolution of small clusters (containing up to 312 carbon atoms) was specifically investigated under the physical conditions of the northern photodissociation region of NGC 7023. These clusters are found to be thermally photoevaporated much faster than they are reformed, thus providing an interpretation for the lowest limit of the interstellar cluster size distribution inferred from observations. The effects of ionizing the clusters and density heterogeneities are also considered. Based on our results, the possibility that PAH clusters could be formed in PDRs is critically discussed.Comment: 14 pages, 14 figures. Astronomy & Astrophysics, accepted for publicatio

ExaViz: a Flexible Framework to Analyse, Steer and Interact with Molecular Dynamics Simulations

International audienceThe amount of data generated by molecular dynamics simulations of large molecular assemblies and the sheer size and complexity of the systems studied call for new ways to analyse, steer and interact with such calculations. Traditionally, the analysis is performed off-line once the huge amount of simulation results have been saved to disks, thereby stressing the supercomputer I/O systems, and making it increasingly difficult to handle post-processing and analysis from the scientist's office. The ExaViz framework is an alternative approach developed to couple the simulation with analysis tools to process the data as close as possible to their source of creation, saving a reduced, more manageable and pre-processed data set to disk. ExaViz supports a large variety of analysis and steering scenarios. Our framework can be used for live sessions (simulations short enough to be fully followed by the user) as well as batch sessions (long time batch executions). During interactive sessions, at run time, the user can display plots from analysis, visualise the molecular system and steer the simulation with a haptic device. We also emphasise how a Cave-like immersive environment could be used to leverage such simulations, offering a large display surface to view and intuitively navigate the molecular system

An empirical analysis of mobile payments and its current situation in the United States of America and the United Kingdom

LAUREA SPECIALISTIC

CubeSat satellite patch antenna designed with 3D printable materials. A numerical analysis

The paper presents a compact patch antenna system designed using 3D printable materials and compatible with any CubeSat satellite structure. Small satellites are transforming the space industry, allowing space access with an important cost reduction for satellite industries and a shorter plan development time compared to bulky satellites. Moreover, using additive manufacturing, it is possible to design specific system components, also with a complex geometry of the inner part, without material wasting. Furthermore, a key point of 3D printing is to allow to go from design to construction straight, having an enormous effect on the supply chain. Generally, CubeSats count on Very High Frequency and Ultra High Frequency communication systems for low bit-rate uplink and downlink. Instead, S-band is among the favourite choices for high bit rates since the frequency range 2.40-2.45 GHz is one of the International Telecommunication Union (ITU) amateur satellite frequency range. An S-band printed antenna system is designed in the present paper, considering the limitations on size and the weight of CubeSat standard. The antenna system is simulated with an electromagnetic CAD, using the polylactic acid as substrate, or polylactide, a thermoplastic polyester widely used in 3D printing

Serial Patch Array Antenna for an FMCW Radar Housed in a White Cane

The design, realization, and test of the transmitting and receiving antennas for an FMCW radar operating between 24 and 24.25 GHz (ISM band), to be housed in a white cane for improving mobility of visually impaired subjects, have been performed. The coaxial-to-microstrip transition necessary for feeding the antennas has been studied together with the characteristics of serial arrays of increasing number of patches. Based on this study, a serial array with 8 patches has been selected for the transmitting and receiving antennas. The realized structures show a reflection coefficient lower than −10 dB in the ISM band. When the antennas are attached to an FMCW radar board, the radar is able to record reflections from a metallic panel up to a 5 m distance

NUOVO APPROCCIO AL BIOMONITORAGGIO: SVILUPPO DI STRUMENTAZIONE INNOVATIVA BASATA SU BIOSENSORI

2005/2006XIX Ciclo1971Versione digitalizzata della tesi di dottorato cartacea