# Young Researcher Meeting

# 4th Young Researcher Meeting, Trieste 2013 – Program

Please download the conference program.

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**June 3**^{rd} - Back to top

**June 3**- Back to top

^{rd}#### 11:00 - Coffee

#### Welcome (Direttore Prof. Guido Martinelli)

- 11:30 - 12:00 Alice Miceli ( Università di Roma, Tor Vergata)

"__Localization of inclusions in prompt gamma activation analysis: a feasibility study__"Prompt gamma activation analysis is a non-destructive neutron technique for isotope analysis. Samples irradiated by neutrons emit gamma rays with energies that uniquely identify the isotopes and chemical elements within the sample. We present a method to localize inclusions in specimens exploiting gamma ray self-absorption, i.e. absorption of gamma radiation within the sample itself. Depending on the position of the inclusion, the gamma rays will be attenuated differently. Using two detectors on opposite sides of the sample, one can measure the ratio of the gamma ray intensities and calculate the approximate position of the inclusion. This method utilizes the full neutron beam area and provides a fast localization of the inclusions along the direction where the gamma-ray detectors are placed. A new detection system to be tested at the INES beamline at the pulsed neutron source ISIS (Oxford, UK) is simulated. The system consists of two back-to-back gamma-ray detectors and two 2D lead collimators located immediately in front of the detectors. Geant4 Monte Carlo simulations of the beamline were carried out to model gamma spectra from Fe and Al test samples with Cu and Fe slabs. Differences between the actual and reconstructed position of the slabs were ≤ 0.1 cm for all the studied configurations.

- 12:00 - 12:30 Elisa Rojatti (Università di Pavia)

"__Watch Dog detector for beam diagnostic in hadrontherapy application__"The CNAO (Centro Nazionale di Adroterapia Oncologica) is the first Italian Centre for deep hadrontherapy. Patients are treated using proton and carbon ion beams accelerated by a 25 m diameter synchrotron. An elaborated beam control is required to ensure patient safety and a correct dose delivery to the tumor volume. For this purpose many beam diagnostic devices have been developed. This work presents a particular beam detector, named “Watch Dog”, that will be installed at the end of the CNAO extraction lines. It is a beam monitor based on two couples of scintillating fibers connected to avalanche photo-diodes. The fibers are displaced on the horizontal and the vertical beam planes and can either stay at beam spot borders as a ‘watch-dog’ or scan the beam cross section to reconstruct the profile. In the ‘watch dog’ mode it doesn’t perturb the beam and it could be used during patient treatment to monitor on-line the beam position at the Scanning Magnets entrance. The goal is to follow slow beam displacements with time or to give an interlock signal in the case the beam position is out of the nominal range. Until now the hardware has been designed, built and assembled and a first release of motion and data acquisition software has been prepared. Preliminary tests in lab have been performed and beam tests are planned shortly.

- 12.30 - 13.00 Emanuela Pusceddu (IBIMET-CNR)

"__Morphological investigation and physical characterization of ancient fragments of pyrogenic carbon__"There is increasing attention on the potentials of using pyrogenic carbon as a climate mitigation strategy. The concept is that of transforming green biomass into a carbon rich product by means of pyrolysis and pyrogasification. This material, that is often called "biochar" contains substantial amonts (60-90%) of pyrogenic carbon, which is a recalcitrant material which is hardly decomposed by means biotic and abiotic oxidation. The mitigation potential of biochar is associated to the fact that carbon is not easily returned back to the atmosphere, even after very long incubation times into the soil. In a recent study, Woolf et al. (2010) quantified the theoretical C sequestration potential of biochar following its incorporation into agricultural soils as 1.8 Gt C per year. But much remains to be understood on the long term decomposition of pyrogenic carbon. Is the carbon contained in biochar lasting for decades, centuries or millenia? Several studies have been addressing this question while trying to understand the fate of pyrogenic carbon in the soil, in a quantitative way. But only a few actually considered materials that were produced in the past and most of those that did it, were finally unable to estimate the fraction of Carbon that was oxidized on centennial time scales. We have recently found old deposits of charcoal in soils of the Eastern Alps (Trentino, Val di Pejo) and those were exactly dated at 1859 by means of a dendroanthracological approach. We have investigated carbon decomposition in those soils and reliably calculated the fraction of C that was lost over 155 years. Part of our study was focused on the morphological characterization of several fragments of charcoal, using scanning electron microscopy (SEM). Such study enabled the discovery of specific morphological features of tracheids in the old charcoal, which were tentively associated to a differential oxidation of the structures that were created during carbonization from lignine and cellulose. A series of lab tests was then made to reproduce the same type of transformation in modern charcoal, by means of deliberated rapid oxidation. This work illustrates the results of that specific study, finally highlighting our most recent understanding on long term degradation of charcoal, in soils. We consider that those results may contribute to the ongoing debate on the best, most suitable geo-engineering strategies that can potentially enable effective and sustainable carbon sequestration in agricultural soils, using biochar.

Reference: Woolf et al., Nature Communication, 2010

#### 13.00 - 13.30 Introduction to posters

- Awni Al-Hourani: "Spin Polarization Transfer in Colloidal Magnetic-Plasmonic Au/Iron Oxide Hetero-Nanocrystals"
- Marco Di Stefano: "Colocalization of coregulated genes: a steered molecular dynamics study of human chromosome 19"

#### 13.30 - 14.30 Lunch

- 14.30 - 15.00 Alessio Rocci (Università di Padova)

"__On first attempts to reconcile Quantum Theory with Gravity__"In his 1916's first paper on gravitational waves Einstein began to speculate on interactions between Quantum Theory principles and the postulates of Maxwell's theory and his theory of Gravitation. With this contribution Einstein has stimulated a lot of similar speculations, more or less technical, during the dawn of Quantum Mechanics. These speculations have culminated with the first attempt to quantize the gravitational field, that was provided by Rosenfeld in 1930. In this talk we briefly summarize what happened in this first period (1916-1930), in particular we consider how the de Broglie-Schroedinger school tried to face the problem of how to reconcile wave mechanics and Gravity, with a focus on five-dimensional farm and its farmer Prof. Oskar Klein. These attempts should be looked as the pre-history of quantum field theory in a curved background.

- 15.00 - 15.30 Matteo Rossi (Università di Pavia)

"__Quantum Hypergraph States__"The class of quantum hypergraph states is introduced and discussed. We show that these n-qubit states can be regarded as a generalization of well-known graph states since they are defined according to an underlying mathematical hypergraph, i.e. a graph where edges connecting more than two vertices are considered. We rove that this class of states describes exhaustively the states employed in quantum algorithms, such as Deutsch-Jozsa’s and Grover’s. Finally we discuss some possible further developments, especially in connection with one-way quantum computing.

- 15.30 - 16.00 Angelo Russomanno (SISSA)

"__Synchronization of observables with a periodic driving in Quantum System: phase coherence behind an apparent paradox__"In this talk I discuss some apparently paradoxical phenomena we have recently found. First of all we see that, under very general conditions, when a closed many body quantum system is driven time-periodically, after a transient, the observables become time-periodic and synchronized with the driving. Such an effect is common in systems -- both classical and quantum -- interacting with an environment (a simple example is the damped-driven harmonic oscillator) but is totally unexpected in Hamiltonian dynamics. We show that this phenomenon, commonly associated with loss of phase coherence, in our case strictly depends on quantum interference effects. Quite remarkably, the synchronized observables keep memory of the initial state; nevertheless the state in the Hilbert space gets no synchronization. We show numerical results for the Quantum Ising Chain in transverse field undergoing both a global and a local periodic driving of the transverse magnetization. We conclude with another apparent paradox stemming from the afore-discussed one: our result is that the energy stays bounded even in the Linear Respone Regime; this contrasts with the Linear Response Theory prediction of a steady energy increase. The solution of this paradox will make clearer the common statement according to which "a many body system acts as its own heat bath''.

- 16.00 - 16.30 Matteo Serra (Università di Cagliari)

"__Einstein-scalar gravity and holography__"The AdS/CFT correspondence provides a very interesting connection between a gravitational theory and a quantum field theory. In this context, black hole solutions with scalar “hair” have acquired a growing interest and importance in the last years. These solutions can in fact describe, holographically, condensed matter-like behavior as phase transitions, superconductivity and hyperscaling violation. We present some of the more recent developments in this topic, and describe the main features of several analytical and numerical solutions of Einstein gravity and Einstein-Maxwell gravity coupled to scalar fields, both from a pure gravitational point of view and from the perspective of the dual field theories.

#### 16.30 - 17.00 Coffee Break

- 17.00 - 17.30 Razieh Emami Meibody (ICTP Trieste)

"__Anisotropic inflation from charged scalar field__"The observational data provided by Planck satellite indicates some deviations from the statistical isotropy, which is one of the fundamental assumptions of the standard model of cosmology. These statistical anisotropies may be achieved by introducing some vector fields during inflation. In this talk, first I consider an inflationary model with U(1) gauge fields and charged scalar field. I show that there exists attractor solution where the anisotropies produced during inflation become comparable to the slow-roll parameters. Then, using the in-in formalism, I obtain the correction to the primordial power spectrum due to these anisotropic sources.

- 17.30 - 18.00 Laura Taddei (Università di Parma)

"__Spherical collapse in Symmetron Models__"The “Symmetron model” is a scalar field model for dark energy in which the scalar field is coupled to matter and it is invariant under reflection symmetry phi-> -phi. The coupling of the symmetron scalar field with matter is such that the symmetry is exact in high density environments, and spontaneously broken when the density drops below a critical value. Deviations from GR are turned on only as a consequence of symmetry breaking. In this presentation, I will discuss the behaviour of this model when the density perturbations become non-linear, in particular using the spherical collapse method. At first, I will show that the collapse depends on the value of the initial radius of the sphere, which separates two different regimes: the “thin-shell” regime, in which the scalar field is zero inside the bubble and is confined only in the background, and the “thick-shell” regime in which the scalar field has the some value everywhere. I will place particular focus on the calculation of the extrapolated linear density contrast at collapse in there two regimes and for different values of the scalar coupling to matter, which is one of the parameters of this model. Then I will continue the discussion of the non-linear aspects of the symmetron model by examining the properties of dark matter halos. Specifically, I will quantify their abundance, i.e. the halo mass function, clustering properties, i.e. the linear bias, to see how they are modified from the standard cosmological constant, cold dark matter model LCDM.

- 18.00 - 18.30 Eloisa Menegoni (University of Heidelberg (ITP))

"__Constraints on variations of the fine structure constant from Cosmological data__"In recent years much attention has been focused on the fine structure constant α mainly because of the observational indication that the fine structure constant was smaller in the past, at cosmological redshifts z = 0.5 − 3.5. On the other hand new and larger galaxy surveys will provide new galaxy weak lensing measurements that, when combined with the CMB experiments (which put constraints on alpha at z=1000), will drastically improve the constraints on cosmological parameters. In this talk I will give an overview on the constraints on alpha we can obtain by using Cosmological data. I discuss present and future cosmological constraints on variations of the ﬁne structure constant α induced by an early dark energy component having the simplest allowed (linear) coupling to electromagnetism. I also present the new results from Planck data on the value of the fine structure constant.

#### Social Dinner

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**June 4**^{th} - Back to top

^{th}

- 09:30 - 10:00 Luca Franci (Università di Parma)

"__Bar-Mode Instability In Relativistic Rotating Stars__"I present results on the dynamics and the onset of the classical bar-mode (m=2) instability of differentially rotating relativistic star models in presence of non zero magnetic fields. The study is carried out performing full 3D ideal magneto-hydrodynamics simulations, in full General Relativity, superimposing to initial (matter) equilibrium configurations purely poloidal magnetic fields of different strength (in the range 10

^{13}-10^{16}Gauss). For all models we observe a sudden formation, and linear growth, of a toroidal magnetic field component that rapidly overcomes the original poloidal one as a consequence of the winding of the magnetic field lines dragged by differential rotation, and hence an amplification of the total magnetic energy inside the star. Magnetic fields of order 10^{14}Gauss or less, have negligible effetcs on both stable and unstable models, while greater magnetic fields are able to completely suppress the hydrodynamical instabilities which are instead present in the un-magnetized case (the treshold being different for the different unstable models). - 10:00 - 10:30 Alberto Zonca (Università di Cagliari)

"__Modeling galactic extinction with dust and 'real' PAHs__"We elaborated an interstellar dust model to reproduce observed interstellar extinction curves. Our model presents two components: i) a classic component regarding dust grains composed by a silicatic core and a carbonaceous mantle (this description is mutuated by the cycle of carbon in the interstellar medium), ii) a molecular component with single and stacked polyciclic aromatic hydrocarbons (PAHs). The latter component is supposed to be the carrier of prominent features of interstellar extinction curves, mainly the bump, attributed to π* ← π transitions, and the FUV rise, attributed to the low energy tail of the σ* ← σ transitions. For the molecular component we exploited two descriptions: i) a simplified one in which we used two lorentzian profiles to mimic π* ← π and σ* ← σ resonances, ii) a detailed one in which we used a superposition of computed quantum photo-absorption cross sections for PAHs in four charge states: anion, neutral, cation and dication. We validated this model reproducing 328 galactic interstellar extinction curves using both descriptions. Despite the large number of parameters we were able to determine some global properties of dust and molecular population, such as the numbers of exploited Si and C atoms and the mean charge of PAHs mixture. But we were not able to get information about individual properties of single PAHs molecules. I will discuss the present results and forthcoming future developments of this promising lines of work.

- 10:30 - 11:00 Stefano Pilo (INAF/Observatory of Rome)

"__The red UV slopes of z~3 Lyman Break Galaxies and implications on dust content and Cosmic Star Formation Rate__"Galaxy evolution is one of the most important topics in modern cosmology. This research field aims at understanding the physical processes through which the cosmic structures are formed out of the nearly uniform distribution of matter of the early Universe. The aim of the study is to estimate an important parameter related to galaxy evolution that is the Cosmic Star Formation Rate that shows the star formation along the cosmic time. Studying Lyman break galaxies (star forming galaxies at high redshift) at z~3 (where CSFR has a peak), is a powerful tool to constrain galaxy evolution models. One of the most important physical properties of these galaxies is actually SFR, the correct estimate of which from the restframe UV photons relies on a detailed knowledge of the dust content of these galaxies. Taking advantages of new deep images acquired by Large Binocular Telescope in U G R optical bands and ULTRAVISTA survey in near infrared bands, and using an innovative technique for photometry and selecting galaxies at highz, I estimated the UV slope of the galaxy Spectral Energy Distribution (SED) for a robust sample of galaxies: this is linked, through simple assumptions, to their dust content, and so I measured the “dust- corrected” SFR. I have found that z~3 LBGs show a higher dust content than the ones at higher redshift. I will also show future prospects implying a comparison with CANDELS database (which images have been acquired by HST telescope). What comes out from this work well fit in the trend for which amount of dust in galaxies decrease with increasing redshift and remarks important challenges both observational and theoretical about the mechanisms of dust formation in the Universe and the evolution of such important physical properties of galaxies along cosmic time.

#### 11.00 - 11.30 Coffee Break

- 11:30 - 12:00 Luciana Renata de Oliveira (Università di Bologna)

"__Energy consumption and entropy production in a stochastic formulation of BCM learning__"The stochastic description of natural phenomena is one of the hallmarks of contemporary Physics, it has been applied to a variety of problems and during the last decade has gained increasing popularity in other fields of Science such as Biology and Medicine. A reason for this expansion is that many biological processes are molecularly-based and hence the role of fluctuations can't be ignored. Chemical master equation models help us to understand and clarify the difference between closed and open systems. The notion of detailed balance (DB) is related to this system's characteristics. If a system is open it will reach after a sufficiently long time, a non equilibrium steady state (NESS) that is sustained by a flux of external energy. We show that two implementations of the BCM learning rule (BCM82*) and (BCM92**) are respectively always in DB and not. We define a one parameter parametrization of the BCM learning rule that interpolates between these two extremes. We compute thermodinamical quantities such as internal energy, free energy (both Helmholtz and Gibbs) and entropy. The entropy variation in the case of open system (i.e. when DB does not hold) can be divided into internal entropy production and entropy exchanged with surroundings. Finally, we show how the entropy variation can be used to find the optimal value (corresponding to increased robustness and stability) for the parameter used in the BCM parametrization.

*Bienenstock, E. L., Cooper, L. N, and Munro, P. W. (1982). Journal of Neuroscience, 2: 32-48.

**Intrator, N. and L. N. Cooper (1992). Neural Networks 5 (1): 3-17 - 12:00 - 12:30 Wenjun Hu (SISSA)

"__Direct evidence for a gapless $Z_2$ spin liquid by frustrating Neel antiferromagnetism__"By direct calculations of the spin gap in the frustrated Heisenberg model on the square lattice, with nearest- (J

_{1}) and next-nearest-neighbor (J_{2}) super-exchange couplings, we provide a solid evidence that the spin-liquid phase in the frustrated regime 0.45 \lesssim J_{2}/J_{1}\lesssim 0.6 is gapless. Our numerical method is based on a variational wave function that is*systematically*improved by the application of few Lanczos steps and allows us to obtain reliable extrapolations in the thermodynamic limit. The peculiar nature of the non-magnetic state is unveiled by the existence of S=1 gapless excitations at k=(\pi,0) and (0,\pi). The magnetic transition can be described and interpreted by a variational state that is built from Abrikosov fermions having a Z_{2}gauge structure and four Dirac points in the spinon spectrum. - 12:30 - 13:00 Yan-hua Hou (INO-CNR BEC Center e Universita' di Trento)

"__First and second sound in a highly elongated Fermi gas with resonant interactions__"We consider a Fermi gas at unitary trapped by a highly elongated harmonic potential and solve the equations of two fluid hydrodynamics at finite temperature. The propagation of sound waves as well as the discretized solutions in the presence of axial trapping are considered. The relevant thermodynamic functions entering the hydrodynamic equations are discussed in the superfluid and normal regimes in terms of universal scaling functions. Both first sound and second sound solutions are calculated as a function of temperature and the role of the superfluid density is explicitly pointed out. The density fluctuations in the second sound wave are found to be significantly large as a consequence of the coupling with first sound. Emphasis is also given to the comparison with recent experimental data.

- 13.00 - 13.30 Mirco Panighel (Universita' di Trieste)

"__Tunneling and photoemission spectroscopy of metal- organic molecules on metallic substrates__"There is huge interest in organic-inorganic interfaces due to their flexibility and peculiar properties. Organic molecules such as porphyrins and phthalocyanines have specific light absorption and charge conversion properties and, in addition, they have a core macro-cycle able to bind a variety of metal ions. The properties of this kind of molecules have recently been exploited in different fields: for instance when adsorbed on metal surfaces their molecular framework tunes their interactions with the substrate constituting ordered structures, and the central metal ion gives to the molecule specific electronic and magnetic properties, which are promising for applications in emerging fields like spintronics and molecular electronics as building blocks for organic devices. The combined results of tunnelling spectroscopy (scanning tunneling spectroscopy and density of states mapping) with synchrotron radiation techniques (x-ray photoemission spectroscopy as well as absorption spectroscopy) allow a complementary and deep understanding of electronic properties of these systems. Furthermore low temperature measurements and break junctions techniques permit to investigate their magnetic and charge transport properties.

#### 13.30 - 14.30 Lunch

- 14.30 - 15.00 Mauro Aresti (Università di Cagliari)

"__Ultrafast Optical Spectroscopy Techniques applied to colloidal semiconductor nanocrystals__"Colloidal semiconductor nanocrystals can be the material of choice for a wide variety of optical applications because of their tuneable optical gaps and their easy processability. Nanocrystals can be used as light absorbers and emitters in optoelectronic devices such as Light Emitting Diodes, photodetectors, solar cells and other similar optoelectronics devices. I apply ultrafast optical spectroscopy techniques to investigate the photophysics of different nanostructured materials. In particular, these novel nano-materials will emit or absorb light efficiently so that they can be used in actual applications for everyday life. The study starts from the well known core/shell nanocrystals CdSe/CdS, that have high quantum efficiencies; but under steady-state illumination the intensity of the light emitted from this nanocrystals randomly blinks over time. Understanding these phenomena is important, because this issue limits the use of these materials in real applications. Complex nanostructures as octapod shape of CdSe/CdS nanocrystals are also been studied: these are very promising in photovoltaic applications. For the characterization of these nanocrystals I have used time-resolved photoluminescence spectroscopy by means of streak camera at picosecond and transient absorption spectroscopy at femtosecond also known as pump probe technique. I also had the opportunity to develop a novel optical technique: Variable Pulse Rate Photoluminescence, that allows to create in a controlled way and to study charges and traps in nanocrystals.

- 15:00 - 15:30 Francesco Ricci (Universita' di Cagliari)

"__Polarization-driven magneto- and electro-resistance in multiferroic junctions__"Multiferroic junctions combining metallic ferromagnets and insulating ferroelectrics are a currently fashionable avenue to obtain electroresistance and magnetoresistance modulation of tunneling as well as in-plane transport exploiting polarization switching in the ferroelectric interlayer. Using first-principles density functional calculations, we investigated a thick asymmetric SrRuO3/PbTiO3/SrRuO3 multiferroic junction with both PbO/RuO2 and PbO/TiO2 interfaces. We find a substantial residual depolarization field in the ferroelectric, despite the effective screening by SrRuO3, which is both electronic and ionic in nature. In the two states of polarization of the ferroelectric, the local potential seen by tunneling electrons is different, leading to resistivity asymmetry under polarization switching. The large ferroelectric monopoles at the interfaces carry a significant spin polarization, again different in the two polarization states. We measure the asymmetry in tunneling simply comparing our calculated 1D averaged local potential, while we give a quantitative description of the in-plane transport by calculating the spin-selective resistivity as a function of polarization direction, in the Bloch-Boltzmann approach.

- 15.30 - 16.00 Pietro Bonfa' (Universita' di Parma)

"__Superconducting-to-magnetic transition driven by magnetic impurities in the optimally doped La-1111 iron-based superconductor__"For iron pnictides superconductors it is mainly believed that magnetic fluctuations are predominantly responsible for the Cooper pair formation. Magnetic impurities are useful candidates to probe this hypothesis. When introducing impurities the consequent hole or electron doping, both outside and inside the Fe layers, controls superconductivity [1]: this mechanism is at play in Mn-doped NdFeAsO0.89F0.11 and Co-doped RFeAsO0.89F0.11 (R=Nd, La), where Fe substitutions of a few percent destroy superconductivity [2,3]. In these cases both the impurity scattering potential and the doping effect contribute to the suppression of TC. Here we investigate the specific extraordinary poisoning effect of Mn [3] on the superconducting ground state of LaFe1-xMnxAsO0.89F0.11 where only 0.1% of Mn (x=0.001) is enough to destroy superconductivity without modifying the doping degree of the compound. A phase diagram of this system as a function of Mn doping for low dopant concentration is sketched by means of local spectroscopic techniques. A detailed zero and transverse field (ZF&TF) muon spin rotation (μSR) investigation of the magnetic and the superconducting ground states reveals that when the SC ground state disappears for doping x=0.001, a static magnetic order in the iron plane arises. Transverse Field μSR (TF-μSR) analysis allows to characterize the SC ground state showing that the superfluid density is strongly depressed by the Mn addition. Moreover, 75As NQR measurements show that before re-entrant magnetic order is established, afm correlations, visible in an increase of 1/T1T at low temperatures, preexist also in the superconducting phase. All these results and their implication for the superconducting pairing mechanism will be discussed in the framework of the recently published theoretical efforts to characterize the effect of impurities with respect to the the order parameter properties [4].

[1] A.S. Sefat et al., Phys. Rev. Lett. 101, 117004 (2008)

[2] E. Satomi et al., J. Phys. Soc. Jpn. 79, 094702 (2010)

[3] M.Sato et al., J. Phys. Soc. Jpn. 79, 014710 (2010)

[4] Y. Wang et al., Phys. Rev. B 87, 094504 (2013)