Heat-charge mixed noise and thermoelectric efficiency fluctuations

The close relationship between the noise and the thermoelectric conversion is studied in a quantum dot using a quantum approach based on the non-equilibrium Green function technique. We show that both the figure of merit and the efficiency can be written in term of noise and we highlight the central role played by the correlator between the charge current and the heat current that we call the mixed noise. After giving the expression of this quantity as an integral over energy, we calculate it, first in the linear response regime, next in the limit of small transmission through the barriers (Schottky regime) and finally in the intermediate regime. We discuss the notion of efficiency fluctuations and we also see here that the mixed noise comes into play.Comment: Proceeding of the UPON 2015 conferenc

Getting information from the mixed electrical-heat noise

We give a classification of the different types of noise in a quantum dot, for variable temperature, voltage and frequency. It allows us first to show which kind of information can be extracted from the electrical noise, such as the ac-conductance or the Fano factor. And next, to classify the mixed electrical-heat noise, and to identify in which regimes information on the Seebeck coefficient, on the thermoelectric figure of merit, or on the thermoelectric efficiency can be obtained.Comment: Proceeding of the ICNF 2017 conference, IEEE, International Conference on Noise and Fluctuations (2017

Dynamical photo-induced electronic properties of molecular junctions

Nanoscale molecular-electronic devices and machines are emerging as promising functional elements, naturally flexible and efficient, for next generation technologies. A deeper understanding of carrier dynamics in molecular junctions is expected to benefit many fields of nanoelectronics and power-devices. We determine time-resolved charge current flowing at donor- acceptor interface in molecular junctions connected to metallic electrodes by means of quantum transport simulations. The current is induced by the interaction of the donor with a Gaussian-shape femtosecond laser pulse. Effects of the molecular internal coupling, metal- molecule tunneling and light-donor coupling on photocurrent are discussed. We then examine the junction working through the time-resolved donor density of states. Non-equilibrium reorganization of hybridized molecular orbitals through the light-donor interaction gives rise to two phenomena: the dynamical Rabi shift and the appearance of Floquet-like states. Such insights into the dynamical photoelectronic structure of molecules are of strong interest for ultrafast spectroscopy, and open avenues toward the possibility of analyzing and controlling the internal properties of quantum nanodevices with pump-push photocurrent spectroscopy

Conceptual metaphor in teaching/learning electric circuits for student teachers of primary school and kindergarten

Integration between cognitive linguistic aspects and physics has been performed in the Physics Education course of the Master's Degree for prospective primary teachers at the University of Udine in Italy. Conceptual metaphors have been introduced to the students, who were then invited to apply the ideas to the electric circuits. In this contribution we present some relevant results of this activity pointing out how students have worked with metaphors, gaining better conceptual understanding on the disciplinary topic

Non-orthogonal Theory of Polarons and Application to Pyramidal Quantum Dots

We present a general theory for semiconductor polarons in the framework of the Froehlich interaction between electrons and phonons. The latter is investigated using non-commuting phonon creation/annihilation operators associated with a natural set of non-orthogonal modes. This setting proves effective for mathematical simplification and physical interpretation and reveals a nested coupling structure of the Froehlich interaction. The theory is non-perturbative and well adapted for strong electron-phonon coupling, such as found in quantum dot (QD) structures. For those particular structures we introduce a minimal model that allows the computation and qualitative prediction of the spectrum and geometry of polarons. The model uses a generic non-orthogonal polaron basis, baptized the "natural basis". Accidental and symmetry-related electronic degeneracies are studied in detail and are shown to generate unentangled zero-shift polarons, which we consistently eliminate. As a practical example, these developments are applied to realistic pyramidal GaAs QDs. The energy spectrum and the 3D-geometry of polarons are computed and analyzed, and prove that realistic pyramidal QDs clearly fall in the regime of strong coupling. Further investigation reveals an unexpected substructure of "weakly coupled strong coupling regimes", a concept originating from overlap considerations. Using Bennett's entanglement measure, we finally propose a heuristic quantification of the coupling strength in QDs.Comment: 17 pages, 11 figures, 3 table

Training Prospective Primary and Kindergarten Teachers on Electric Circuits Using Conceptual Metaphors

The awareness and use of conceptual metaphors available in ordinary language should be a relevant part of teaching strategies, yet it is still rather neglected in teacher education. With a specific activity, we integrated a class of prospective kindergarten and primary school teachers on electric circuits with a reflection on the cognitive and linguistic aspects of metaphor. To understand how effective this integration proved to be, both in terms of learning and in terms of developing teaching skills, we conducted a single case study with a mixed qualitative–quantitative methodol-ogy. Student teachers were invited to analyze and discuss expressions on electric circuits selected from those they themselves had formulated at an earlier time. Here, we present some relevant results from the analysis of the students’ elaborations, highlighting how they worked with metaphors. They demonstrated a better understanding of the subject matter and greater awareness of teaching as well, in particular for what concerns the use of language and identifying and overcoming implicit ideas

A NEW CLASS OF NON-CODING RNA CONTROLS THE DNA DAMAGE RESPONSE AND DNA REPAIR

DNA is the most precious molecule in our cells, thus it has to be protected from damage and alterations and, if damaged, it has to be repaired efficiently. The DNA damage response (DDR) is a signaling cascade that follows the generation of a lesion in the DNA double helix and promptly arrests cell proliferation in order to attempt DNA repair. It has been proposed that mammalian genomes are pervasively transcribed, also in non-coding regions. Non-coding RNAs (ncRNAs) have been involved in an increasing number of cellular events and some of them are processed by members of the RNA interference (RNAi) pathway. So far, RNAi and DDR pathways have not been demonstrated to directly interact. During my PhD, I contributed to uncover an unexpected layer of DDR regulation by a new class of DICER- and DROSHA-dependent small non-coding RNA, named DDRNA. DDR foci stability is sensitive to RNA polymerase II inhibition and to RNase A treatment. Incubation of RNase A-treated cells with DICER- and DROSHA-dependent RNA products restores focal accumulation of DDR factors. DICER and DROSHA are indeed necessary to trigger DDR upon exogenous DNA damage in human cells, and DICER processing activity is necessary to activate DDR. Moreover, DICER and DROSHA knockdown impacts on checkpoint activation and allows senescent cells to re-enter S-phase. Differently, inactivation of GW182, a component of the RNAi machinery involved downstream of DICER and DROSHA in mRNA translational control, does not impact on DDR foci formation and detection. In a mammalian cell system in which a single DNA double-strand break can be generated at a defined exogenous integrated locus, DDR focus formation requires site-specific RNA molecules. RNA deep sequencing confirmed the presence of 22-23-nucleotide sequence-specific transcripts arising from the damaged locus, which are DICER-dependent. These DDR-regulating RNAs (DDRNAs) act at the first steps of the DDR cascade, in an MRN-dependent manner and have an impact also on DNA damage repair. Importantly, DDRNAs, both chemically synthesized or generated in vitro by DICER cleavage, are biologically active and antisense LNA oligonucleotides reduce DDR activation in living cells. Finally, by the use of fluorescently labeled molecules, DDRNAs have been demonstrated to localize at the site-specific damaged locus. Collectively these results suggest an unanticipated direct role of DICER and DROSHA in the production of small ncRNAs that control DDR activation at sites of DNA damage. Given the known tumor suppressive functions of DDR and the implication of its activation in a number of biological relevant processes, such as senescence, this discovery may have a significant impact on our understanding of ageing and cancer