Physics of Complexity@ ISC - Sapienza

Physics of Complexity@ ISC - Sapienza

Rome, 2014-2015 Rome, 2014-2015

Physics of Complexity @ ISC - Sapienza

The Institute of Complex System (ISC) of the National Research Council(CNR) was created on February 2010.

The Unit Sapienza of ISC has been built upon researchers previouslyinvolved with the National Institute of Material Physics (INFM) within theDepartment of Physics. For this reason, since the very beginning, theirresearch has been deeply interconnected with the activities of the Departmentof Physics.

Since 2010 the Unit has grown and its interests expanded in severaldirections, while the basic mission remained unchanged: the understanding ofall those systems where the mutual interactions between a large number ofcomponents cannot be reduced to an effective single-element scheme. Theresulting complexity manifests itself in a wide variety of emerging phenomenaoccurring in different contexts, ranging from social networks to granularmaterials, from (soft) colloids to (hard) electronic systems, from collectivemotions of animal groups to non-linear systems.

In this booklet each staff member of the Unit presents some of his/heractivities, with the aim to give an overview of the research carried outpresently at ISC-Sapienza.

Rome, November 2014

For further information please visit our web sites:

www.isc.cnr.it

www.sapienza.isc.cnr.it

Andrea Baldassarri

contacts

Andrea.Baldassarri@roma1.infn.itOffice: Fermi Building, 510https://aquilante.phys.uniroma1.it/~andreab

keywords

● Percolation● Granular materials● Stochastic processes

Rocky coast erosion and percolation theory

As shown by a minimal numerical model,percolation theory can be used as a guide todecipher the physics of rocky coast erosionand could provide precise predictions to thestatistics of cliff collapses. I'm interested inpossible applications of percolation theory ingeomorphology, as revealed by irregulargeometries or anomalous statistics.

Friction is a very old, but still open field ofresearch, relevant from the physics at nano-scaleto earthquakes. The friction response of agranular material could be very fluctuating, due tothe anomalous stress propagation in the material.This systems represent an interesting laboratory,both experimentally and theoretically, for theintroduction of new models and concepts.

Irregular, bursty dynamics can be modeledvia simple stochastic processes, revealingunexpected connections between differentphysical systems (crackling noise).

Avalanche dynamics and crackling noise

Friction in granular materials

Lara Benfatto

contacts

Lara.Benfatto@roma1.infn.itOffice: Marconi Building, room 110https://www.roma1.infn.it:~lbenfat

keywords

● Theory of Many-Body Systems● Superconductivity in low dimensions● Materials with Novel Electronic Properties

The inhomogeneous local DOS measured by STMshows an universal probability distribution of thelocal SC order parameter when properly rescaled

A typical example of competing states isprovided by strongly disorderedsuperconductors: here disorder tendsto order the charge, by localizing theelectrons, and pairing tends to order theglobal electronic phase, i.e. to form thes u p e r c o n d u c t i n g s t a t e . A s acompromise, the system develops anintrinsic inhomogeneous phase withunusual glassy properties.

G.Seibold et al. Phys.Rev.Lett.108, 207004 (2012).G. Lemarie et al. Phys. Rev. B 87, 184509 (2013).

The competition and interplay betweent w o d i f f e r e n t p h e n o m e n a , i . e .magnetism and superconductivity, isalso the key issue for the understandingof the new generation of iron-basedhigh-temperature superconductors. Inthese materials the multiband structureand the interband nature of the pairinglead to a plethora of new phenomena,unexpec ted in o ther mu l t ibandsuperconductors. In addition theelectron pairing in these materials turnsout to be very robust against disorder, astill unexplained phenomenon thatrepresent nowadays a promising rootfor future applications.

The understanding of the electronic properties of complex solid-state systems,where one observes the competition between different phenomena, requires todevelop and implement a modern quantum-field theory approach. This includesseveral analytical techniques, ranging from a conventional perturbative expansion tothe derivation of the quantum functionals for the collective degrees of freedom

NbN disordered films

UnconventionalHa l l e f f ec t i npnictides

L. Fanfarillo et al.PRL 109,096402(2012).

Emmanuele Cappelluti

contacts

emmanuele.cappelluti@roma1.infn.itOffice: Fermi Building, room 109, Ph.: 06-4991-3488Office: ISC, CNR, v. dei Taurini 19, Ph.: 06-4993-7453http://pil.phys.uniroma1.it/~emmcapp

keywords

● Many-Body Interactions and Theoretical Physics in Condensed Matter● Superconductivity and collective phenomena● Graphene and low-dimensional systems

My research activity investigatesthe appearance of many-bodyphenomena o f fundamenta lphysics in a variety of specificcondensed matter systems.Examples of open research lineswhere Master theses are available:

Graphene and post-graphenecompoundsTheoretical modelling of electronic,lattice, thermodynamical, optical,and magnetic properties of two-dimensional materials (graphene,dichalcogenides,...).

Interactions and Pairing in Iron-based SuperconductorsMicroscopical description of thescattering and pairing mechanismsin the normal state (transport,optical properties) and in thesuperconduct ing s ta te (gapsymmetry).

Lat t ice /spin polarons andInterplay between electron-lattice and magnetic interactionsMechanisms and properties ofcomplex objects (polarons) wheredifferent degrees of freedom(electron, lattice deformation, spin)are entangled at a local scale.Itinerant vs. trapped states.

Spontaneous broken-symmetryphases in layered compoundsNematic, charge and bond-density-waves driven by Hubbard-Hundinteract ions in layered two-dimensional materials.

Claudio Castellano

contacts

claudio.castellano@roma1.infn.itOffice: Via dei Taurini 19, 4th floor, room 409http://sites.google.com/site/claudiocastellanohome/home

keywords

● Interdisciplinary applications of statistical physics● Complex networks● Dynamics of social systems

Statistical physics approach tosocial dynamicsIn recent years it has become widelyrecognized that many large-scale phenomenaobserved in soc ia l sys tems are the"macroscopic" emergent effect of the"microscopic" behavior of a large number ofinteracting agents. This has led to theintroduction of elementary models of socialbehavior (opinion dynamics, cultural andscientific evolution, language change). Many ofthese models are relatives of models that arestudied in modern statistical physics, and it isnatural to approach them using the sameconcepts and tools successfully applied inphysics.

C. Castellano et al., “Statistical physics of social dynamics”,Rev. Mod. Phys. 81, 591 (2009)

F. Colaiori et al., “A general three-state model with biasedpopulation replacement: analytical solution and application tolanguage dynamics”, Phys. Rev. E (to appear).

Spreading processes oncomplex networksDynamical processes have been studied fordecades on regular lattices and their behavioris generally well understood. When suchprocesses take place on a complex topology,what is the effect of the disordered interactionpattern on their phenomenology? In recentyears I have been in particular involved in theinvestigation of the behavior of spreadingprocesses, which range from infectiousdisease epidemics to “social contagion”, i.e.,

information diffusion or meme propagation.Complex networks topology has a very strongimpact on epidemic processes, facilitatingspreading and increasing the r isk ofpandemics. Nontrivial effects are responsiblefor this vulnerability and their understandingchallenges established theoretical approaches.

The study of epidemic-l ike spreadingprocesses in the social domain, spurred bythat the “big data” revolution is a very activeand promising field for future research.

C. Castellano and R. Pastor-Satorras, “Threshold for epidemicspreading in networks”, Phys. Rev. Lett. 105, 218701 (2010).

M. Boguna' et al., “Nature of the Epidemic Threshold for theSusceptible-Infected-Susceptible Dynamics in Networks”,Phys. Rev. Lett. 111, 068701 (2013).

R. Pastor-Satorras et al., “Epidemic spreading in networks”,arXiv: 1408.2701 (2014).

Andrea Cavagna

contacts

andrea.cavagna@roma1.infn.it,Office: ISC/CNR - Via dei Taurini 19 – Floor 4th

http://www.sapienza.isc.cnr.it/component/content/article/68.html

keywords

● Collective Behavior in Biological Systems● (Non-Equilibrium) Statistical Mechanics● Inference, Modeling & Simulations

Collective Behavior in BiologicalSystemsThe basis of our overall methodology islinking the experimental data (observedbehaviour) with the theories explaining theinteractions rules governing large animalgroups. This broad mandate requires aninterdisciplinary approach ranging fromfield experiments, to computer vision, tostatistical physics. In general, we havesplit our focus in two areas: i)experimental data gathering andprocessing; ii) data analysis and theory.Our experimental work is carried out in thenatural habitat of the animal we arestudying. We use multiple synchronizedhigh speed cameras to capture imagesequences of the aggregation. By usingnovel computer vision algorithm, we arethen able to reconstruct the 3D trajectoriesof each individual in the group. Our dataanalysis follows a theoretical approachinspired by the principles of statisticalphysics.

Supercooled liquids and theglass transitionI am working on devising new methods todetect a growing static correlation length indeeply supercooled liquids. By usingamorphous boundary conditions wemeasured for the first time athermodynamic correlation length. In sodoing we test the validity of differenttheoretical frameworks of the glasstransition, namely the Adam-Gibbs theoryand the Mosaic (aka Random First Order)theory. We are also trying to measure thesurface tension between differentamorphous phases in deeply supercooledliquids and to establish a link betweenstatic relaxation and dynamicheterogeneities through the concept ofsurface tension. Check my pedagogicalreviews on spin-glasses and supercooledliquids, Spin-Glass Theory for Pedestrians[J. Stat. Mech. (2005) P05012] andSupercooled Liquids for Pedestrians,Physics Reports 476, (2009), P51

figure

Fabio Cecconi

contacts

Fabio.Cecconi@roma1.infn.itOffice: Via dei Taurini, 19 tel:06-4993.7452 http://denali.phys.uniroma1.it/~cecconif/

keywords

● Transport of biopolymers in nanopores● Statistical mechanics of complex systems● Nonlinear Physics and Chaos

Transport of proteinsNanopore technology is the “art” of retrievingchemical and physical information aboutbiomolecules through their transport behavioracross nanopores (nanoscale “holes”) FigB.This field is considered the new frontier ofsingle-molecule manipulation and sequencingwith relevant applications to biology andmedicine. Experiments are becoming veryaccurate and produce a countless number offacts and data which the theory is called toexplain. Main theoretical tools: Stochastic Processes,Model l ing and Simulations, StatisticalMechanics.

Statistical mechanics of complexsystemsUnderstanding complex phenomena like theemergence of collective or auto-organizeddynamics in many-body systems requires tomaster advanced concepts and methods ofstatistical mechanics and stochastic processtheory. Particular important is the modeling ofcomplex systems which f inds severa lapplications e.g. to biology, material science,economic or social phenomena. We areinterested to study complex behaviors ingranular materials and transport processes.

Nonlinear Physics and ChaosNonlinearity is a general element of naturalphenomena and Chaos theory is thesystematic study of the “unexpected” effectsproduced by nonlinearities. In particular, twoinitial conditions differing for an infinitesimalerror, which according to Newton's physicswould yield similar results, can led to vastlydifferent outcomes (Butterfly effect). Thediscovery that unpredictable behaviors areconsistent with deterministic laws changed theway we perceive the world around us. Non-linear physics is the interdisciplinary field thatdevelops mathematical tools and concepts toclassify and characterize: chaotic behaviors, strange attractors and the related fractal structures.

Fig. Transport of a protein by a pulling force

Fig. A strange attractor showing a fractalstructure.

Fig. Chain of nonlinearoscillators considered aparadigm of a complexsystem.

Massimo Cencini

contacts

Massimo.Cencini@cnr.itOffice: CNR, Via dei Taurini 19, IV floor room 412http://denali.phys.uniroma1.it/~cencini

keywords

● Turbulence and transport of fields and particles in turbulent flows● Chaos and dynamical systems● Population dynamics

Transport of swimmingmicroorganisms in turbulence

Typically turbulence is very effective in mixingtransported substances so that quickly theydistribute uniformly in the container (imaginestirring milk into coffee). What does happen tomicroorganisms transported by a turbulentflow? Microorganisms are typically very smalland have the same density of the fluid so thatare expected to follow the fluid elements andthus to mix very efficiently. However, if theycan swim, as bacteria or some species ofalgae, something counterintuitive canhappen, namely they can unmix formingfractal aggregates. T h i s i s b e c a u s eswimming allows cell to escape from fluidtrajectories, inducing a sort of effectivecompressibility. This phenomenon has beenstudied experimentally, in a vortical flow, andnumerically, in a turbulent flow, for gyrotactic microalgae (such as, e.g., Chlamydomonas).

W. M. Durham, E. Climent, M. Barry, F. De Lillo, G. Boffetta,M. Cencini, R. Stocker Nature Comm. 4, 2148 (2013)

F. De Lillo, M. Cencini, W. M. Durham, M. Barry, R. Stocker,

E. Climent, G. Boffetta, Phys. Rev. Lett. 112, 044502 (2014)

Neutral biodiversity models Species abundance distributions and how thenumber of species changes with the area(Species Area Relationships) can becaptured by simple neutral models, with a flat“fitness” landscape. Efficient algorithms havebeen developed to study nontrivial regimes ofsmall speciation rate and large local populationsizes, relevant to microorganisms ecology. Wefound that large local populations give rise to shallower SAR, in accord with field observations.

figure

In the case of fast mutating viruses (e.g., Influenza virus), the virus-host interaction is driven by cross-immunity: after being infected by a strain, the host acquires immunity to a set of other strainsantigenically similar to the infecting one (i.e., triggering the same host immune response). The evolutionary dynamics of viruses is then ruled by their relative antigenic distance. Can we understand the nontrivial relation between antigenic and genetic distance?

Francesca Colaiori

contacts

francesca.colaiori@roma1.infn.itOffice: Fermi Building, 510it.linkedin.com/in/FrancescaColaiori

keywords

● Network Science● Quantitative Linguistics● Biophysics

In all languages, rules have exceptions in the form of irregularities.Since rules make a language efficient, the persistence ofirregularity is an anomaly. How do language systems become rulegoverned? How and why do they sustain exceptions to rules? Frequent words are unlikely to change over time (e.g., frequentverbs tend to maintain an irregular past tense form). What is therole of frequency in maintaining exceptions to rules?C

red

it: I

ll ust

ratio

n / J

ona

than

Sa

rag o

sti

Interdisciplinary researchPhysics as a tool

Social networks have empirically been found to be assortative (i.e.,the degrees of neighboring nodes are positively correlated), whileother networks (e.g., technological, biological) show the oppositepattern (disassortative). Why is that so? How do these patterns change in signed networks, where relationsindicate trust/distrust, friendship/enmity? Do individuals who dislikemany others tend to dislike each other, or do they dislike those whodislike only very few others?

Tools from statistical physics, modeling, analytical approach (whenever possible),simulations, data analysis, web-based experiments.

typical problems

methods

Dynamics of Virus-Host interaction

Rules and Exceptions in Language Dynamics

Structure of Social Networks

Claudio Conti

contacts

claudio.conti@cnr.itOffice: Fermi Building, 108http://www.complexlight.org

keywords

● Photonics and nonlinear optics, experiments and theory● High performance computing● Theoretical physics

The enlightened game of life

Is complexity linked with light? We decide ifsomething is complex or not by observing itss t ruc tu re and hence i n te rac t i ng w i t helectromagnetic waves. Is this fact morefundamental than that? We want to developtheoretical models for assessing the linkbetween light and complexity, starting from thesimplest one: the Conway's Game of Life

Complexity arises when there is disorder andnonlinearity. Photonics is full of examples in whichhighly nonlinear regimes occur in the presence ofdisorder. The case of light-matter interaction inrandom systems is specifically important for anovel class of devices named random lasers. Inour laboratory we study random lasers in bio-templated materials and other complex systems.

Highly nonlinear regimes in optics are formallyidentically to quantum gravity enhancedquantum mechanics, including a generalizeduncertainty principle. Can we simulate quantumgravity in the lab?

Quantum gravity simulation

Random lasers, experimental activity

Andrea Gabrielli

contacts

Andrea.Gabrielli@roma1.infn.itOffice: Fermi Building, office 111http://pil.phys.uniroma1.infn.it/~andrea

keywords

● Stochastic processes and networks for interdisciplinary applications● Networks and complex structures in brain science● Long range interacting systems

Economic complexity: If we study how different countries produce different products, we find data which look in contrast with standard economic theories: differentiation of production appears much more important than specialization for advanced economies. Studying the network structure of world productionthrough a non-linear pagerank-like approach permits to uncover the hidden potential of growth of countries and to classify the technological complexity of products.

Complex structures in brain and NMRHuman brain is one of the most complex object of studyin science and it is characterized by a spatio-temporal multiscale and multilevel structures. Nuclear Magnetic Resonance is the best in vivo tool to study both its 3-d disordered structure and its complex behavior.With this experimental technique, supported by the generalized diffusion theory, we can study thediffusion of water molecules in each cell (i.e. voxel)of a 3-d grid to get 3-d brain mages (DNMR). The same technique is used to analyze the temporal coordination between different regions of thebrain during its functioning (fMRI). Network theory then permits to determine thetopological properties of this functional network and characterize in the best way thefunctional connectivity and coordinated behavior of different brain regions.

Quasi-stationary states in long range interacting systemsParticle systems with long range interactions (e.g. self-gravitating gas) present a peculiarbehavior which differs strongly from standard short range interacting systems both atequilibrium (e.g. ensemble inequivalence, negative specific heat) and far from it. Inparticular their out of equilibrium dynamics is characterized by the presence of quasi-stationary states in which the system gets trapped. They are due to the prevalence ofcollective motion on the two-body collision dynamics which in general drives the system atequilibrium. Its study is still an open issue.

Andrea Gnoli

contacts

Andrea.gnoli@isc.cnr.itOffice: Fermi Building, 012http://www.sapienza.isc.cnr.it/your-details/userprofile/andrea_gnoli.html

keywords

● Granular Materials● Brownian Motors

Granular Materials

Granular materials are studied andused to test various fascinatingtheories in the field of nonequilibrium statistical physics.

Many different experiments havebeen realized in the GranularDynamics Laboratory in the FermiBuilding, ground floor, Room 012.In our experiments grains aremade of steel or plastic beads ofvarious size, in the 1 – 4 mmrange. The beads are kept inmovement by a shaker and variousdifferent regimes are realized(granular gas and liquid) in variousdifferent setups (3d, 2d and also1d). The dynamic of the grains isstudied by high speed camerasand/or probed by intruders.

Brownian Motors

Brownian motors are a class ofdevices that extract useful workfrom noise. Such an extraction,which is impossible in the classicalequilibrium thermodynamicframework, is made possiblethrough the use of granulars thatare, by definition, in nonequilibrium conditions. Therectification of fluctuations ischallenging from the experimentalpoint of view and the final directionof motion is not easily predictedwithout a suitable theoreticalmodel.

José Lorenzana

contacts

jose.lorenzana@roma1.infn.itOffice: Marconi Building, 112http://www.sapienza.isc.cnr.it/component/content/article/112.html

keywords

● Theory of Many-Body Systems● Superconductivity● Emerging materials

Complex SolidsMy main interest are complex solidsintended as materials in which differentphases compete producing interestingcollective behavior. Competition arisebecause interactions and the kineticenergy contribute similarly to the energy,therefore complex solids are nor in theweak nor in the strong coupling regimewhich makes them difficult to treat withconventional perturbative approaches.Competition between phases often leads togigantic responses to externalperturbations which makes complex solidsinteresting for applications. I use many-body numerical and analytical techniquesto model the behavior of system withfascinating properties as high temperaturesuperconductors and multiferroics(materials which have ferroelectric andmagnetic order coupled). My work is oftenclose to concrete experiments performedby partner groups and in the last yearshave been focused on time-dependentphenomena as collective modes ofsuperconductors (including the possibilityto observe the analogous of the Higgsboson in condensed matter), generation ofmagnetic responses with an electric pulseor vice versa and understand the physicsof many-body quantum systems out ofequilibrium.

Many-body physics in real timeIn the last years dramatic technicalprogress have enable experiments wherequantum matter is perturbed and itsevolution is monitored in the femtosecondtime scale. The figure shows experimentsby our partners at Laussane [Mansart et al.PNAS, 110, 4539 (2013)] where thereflectivity as a function of energy ismonitored as a function of time delay afteran impulsive perturbation. Ultrafast timeresolution allows to see lattice vibrations(A and D) and also electronic oscillations(B and E). The material is a hightemperature superconductor and theelectronic oscillations are attributed to thesuperconducting condensate. Modelingthese and related experiments can help tounderstand the mechanism ofsuperconductivity in these materials, one ofthe main open problems in physics.

figure

Marco Montuori

contacts

marco.montuori@roma1.infn.itOffice: Fermi Building, 510http://www.sapienza.isc.cnr.it/statistical-dynamics/statistical-cosmology.html

keywords

● Globular Clusters dynamics● Galaxy interactions

Globular Clusters (GCs) are old starclusters in the galaxy and cornerstonefor our understanding of the formation,structure and dynamics of Milky Way.Last decade has seen the discovery oftidal tails emanating of GC.Tails are anew probe of the potential of the galaxyand its time evolution. Throughnumerical simulation and observationalcomparison we can explore thefeatures of dark halo and its dynamics

Galaxies are recognized as the product ofevolution lasting nearly 14 billion years. Itis clear that many galaxies interact withneighboring ones and galaxy interactionsare believed to be the key evolutionarymechanism, in particular for the early-type.We are studying models and numericalsimulations to understand which are thedominant physical processes which drivestheir evolution and produce the richnesswe observe in the universe

Galaxy interactions

Globular Cluster dynamics

Oriele Palumbo

contacts

Oriele.Palumbo@roma1.infn.itOffice:Physics Dpt, Marconi Building, room 360http://www.sapienza.isc.cnr.it/your-details/userprofile/oriel.html

keywords

● Spectroscopies● Innovative materials for energy storage● Phase transitions

Materials for hydrogen storage

The most promising way to store hydrogen isthe solid state storage, but at present a lot offundamental research is still needed to makesuch solid state tanks satisfactorily compatiblewith the targets of current applications.Best candidates are metal hydrides andcomplex hydrides. A big role in increasingtheir capacity and enhancing the hydriding anddehydriding kinetics is played by the artificialmanipulation, like nanostructuring of thepowders, their mechanical alloying andcatalysing. We study the hydrogenation anddehydrogenation fundamental mechanisms ofsuch novel materials by means of mechanicaland infrared spectroscopies, thermal analysisand ab initio simulation.

A. Paolone, F. Teocoli, S. Sanna. O. Palumbo and T. Autrey,J. Phys. Chem. C 117 129-134 (2013).

A. Paolone, F. Vico, F. Teocoli, S. Sanna. O. Palumbo, R.Cantelli, D.A. Knight, J. Trepovich and R. Zidan,J. Phys. Chem. C 116 16365-16370 (2012).

A. Paolone, O. Palumbo, P. Rispoli, R. Cantelli, T. Autrey, A.Karkamkar, J. Phys. Chem. C Lett. 113 10319-10321 (2009).

Hydrides as new anodes forlithium batteries

The incorporation of lithium by hydridesthrough an electrochemical conversionreaction is a promising alternative to Liintercalation into graphite for next-generationLi-ion cells.This reaction has been proved only for acouple of metal hydrides. We are currentlystudying the applicability of complex hydridesand possible improvements of the hydridesperformances in the cells by means of artificialnanostructuring.

D. Meggiolaro, G. Gigli, A. Paolone, F. Vitucci, S. Brutti,J. Phys. Chem. C 117 22467-22477 (2013).

Annalisa Paolone

contacts

Annalisa.Paolone@roma1.infn.itOffice:Physics Dpt, Marconi Building, room 360http://www.sapienza.isc.cnr.it/your-details/userprofile/paolone.html

keywords

● Spectroscopies● Innovative materials for energy storage● Phase transitions

Ionic liquids and theirinteractions with membranes

Ionic liquids (ILs), which are inorganic saltswith melting point below 100°C areenvironmentally friendly solvents with usefulproperties. Moreover their attractive propertiescan be tuned by variation of the cation andanion. Our research is focused to achieve abetter physical understanding of the ionsinteractions and dynamics within the liquids bymeans of infrared and mechanicalspectroscopies, thermal analysis and ab initiosimulation.The occurrence of phase transitions and theirkinetics is studied too. In particular, it is showed that in the compositesystems usually used for applications, theinteraction with the swelling membranemodifies the physical properties of ILs.

F. M. Vitucci, D. Manzo, M. A. Navarra, O. Palumbo, F.Trequattrini, S. Panero, P.Bruni, F. Croce, A. Paolone,J. Phys. Chem. C 118 5749-5755 (2014).

F. M. Vitucci, F. Trequattrini,O. Palumbo, J.-B. Brubach,P.Roy, A. Paolone, J. Phys. Chem. A 118 8758-8764 (20014).

F. M. Vitucci, O. Palumbo, F. Trequattrini,J.-B. Brubach, P.Roy, F. Croce, A. Paolone, J. Phys. Chem. C under review.

figure

New materials for lithiumbatteries

We investigate the fundamental properties ofnew materials considered as promising as highenergy density electrodes for lithium batteries,such as LiNi

0.5Mn

1.5O

4 (LNMO) or LiCoPO

4

(LCPO). We studied the disorder of LNMO bymeans of EXAFS, the vacancy dynamics inLNMO by anelastic spectroscopy and theinfrared phonon spectrum of LCPO.

G. Greco, S. Brutti, F. M. Vitucci, L. Lombardo, M. Koentje, A.Savoini, A. Paolone, S. Panero, J. Phys. Chem. Cdoi:10.1021./jp5063622.

F. M. Vitucci, O. Palumbo, A. Paolone, R. Cantelli, S. Brutti,S. Panero, J. Alloys Compds. 604 83-86 (2014).

S. Brutti, J. Manzi, D. Di Lecce, F. Vitucci, A. Paolone, F.Trequattrini, S. Panero, Mat. Lett. under review.

Alberto Petri

contacts

Alberto.petri@isc.cnr.itOffice: Fermi Building, 109http://old.isc.cnr.it/ita/staff/petri/

keywords

● Dynamics of granular matter● Disordered materials● Complexity in society, biology and economics

Topic 1In our world, granular matter is moreubiquitous than crystals, however itsdynamics is much less understood.Grains also provide a laboratorymodel for earthquakes and dissipativeprocesses. We try to improve ourunderstanding of the collectivedynamics of grains performinglaboratory experiments and numericalsimulations, and try to describe it bymeans of stochastic processes.

Topic 2Structural phenomena occurring indisordered materials often bring

Topic 3Understanding the dynamicsunderlying human andbiological activities is difficult.However the now availablelarge amount of data provideslot of information. We arepresently investigating themutual import-export relations ofworld-wide countries, pointingout analogies with someecological systems.

the features of criticality, i.e.long range correlations and selfsimilar patterns, like forexample in the pattern of apropagating crack. Despite theircomplexity, it is often possibleto understand and describethese phenomena by means ofsimple models like cellularautomata and lattice gas.

Andrea Puglisi

contacts

Andrea.puglisi@roma1.infn.itOffice: Fermi Building, 406http://denali.phys.uniroma1.it/~puglisi/welcome.html

keywords

● Granular materials● Out-of-equilibrium statistical physics● Brownian motors

Granular materialsGranular media are systems madeof many “grains” (particles from0.1mm or larger) which loseenergy when interacting. They area fascinating testground for manyrecent theories in out-of-equilibrium statistical physics (seebelow). Here we study thosesystems by numerical simulations,kinetic theories and experiments.You can have a look to our lab atthe ground floor of Fermi Building,Room 012.

Out-of-equilibrium statisticalphysicsEquilibrium statistical physics failsin many systems where currentsand dissipation appear (turbulence,forced fluidodynamics, aggregateof self-propelled particles, opensystems, etc.). Many alternativeapproaches exist, such ashydrodynamics and kinetic theory,e.g. the Boltzmann equation.

Sometimes these systems are also“small” and for this reasonfluctuations can be very large: thetheories of probability, stochasticprocesses, and large deviations,become – therefore - essentialtools.

Brownian motorsThey are small objects that“rectifies” fluctuations, obtainingwork from heat. We study modelsand experimental examples,showing in which (non-equilibrium)conditions such a rectification maybe optimized.

Antonio Scala

contacts

Antonio.Scala@roma1.infn.itOffice: Fermi Building, 104https://sites.google.com/site/antonioscalaphys/

keywords

● Complex Networks: Critical Infrastructures, Social Networks● Statistical Mechanics: Energy Landscapes, Soft Matter● Computational Physics: Hard body simulations, Monte Carlo

Complex Networks and Power Grids

Electric power-systems are one ofthe most important criticalinfrastructures. We apply statisticalmechanics to understand emergingphenomena in power grids

Self Healing Networks

We study self-healing models ofcomplex networks modelling.Obvious applications are toinfrastructural networks like gas,power, water, oil distribution.

Social Networks

We focus on data-drivencomputational models of complexsocio-cognitive systems: spread ofinformation and opinions, socialhuman behavior, evolution ofsocial networks. We aim todevelop innovative mathematicalmodels and computational tools tobetter understand, anticipate andcontrol massive social phenomenawith a complex systems approach.

publications● Abruptness of Cascade Failures in Power Grids

Scientific Reports 4, 3694

● Self-Healing Networks: Redundancy andStructureDOI: 10.1371/journal.pone.0087986

● Opinion dynamics on interacting networks:media competition and social influenceScientific Reports 4, 4938

Vito D.P. Servedio

contacts

Vito.Servedio@roma1.infn.itOffice: Fermi Building, 505http://pil.phys.uniroma1.it/~servedio

keywords

● Opinion Dynamics, Quantitative Linguistics● Citizen Science and Human Computation● Learning Dynamics

The dynamics of correlated novelties

Novelties are commonplace in daily life. They arealso fundamental to the evolution of biologicalsystems, human society, and technology. Byopening new possibilities, one novelty can pave theway for others in a process that Kauffman hascalled “expanding the adjacent possible”.

The Web has progressively acquired the status of aninfrastructure for social computation allowing researchers tocoordinate the cognitive abilities of human agents bysteering the collective user activity towards predefinedgoals. This general trend is triggering the adoption of web-games as a very interesting laboratory to run experimentswhenever the contribution of human beings is cruciallyrequired for research purposes.

Each sphere of knowledge could be depicted as a networkof correlated items. By properly exploiting theseconnections, innovative and more efficient learningstrategies could be defined, possibly leading to a fasterlearning process and an enduring retention of information.

Statistical modeling of learning paths

Web-based social computation

http://www.xtribe.eu

F. Tria et al., Sci.Rep. 4, 5890 (2014)

Massimiliano Viale

contacts

massimiliano.viale@cnr.itOffice: Fermi Building, Room 414, Floor4th

http://www.sapienza.isc.cnr.it/your-details/userprofile/126.html

keywords

● Collective Behavior in Biological Systems● (Non-Equilibrium) Statistical Mechanics● Inference, Modeling & Simulations

From bird flocks to fish schools, from insect swarms tocell colonies, collective behaviour is a very widespreadphenomenon in many biological systems.It is hard to define, but easy to recognize. What are the mechanisms regulating collective behaviourin biological systems?

The aim of my work is to understand the collective behaviourexhibited by flocks of starlings (Sturnus vulgaris) and swarmsof non-biting midges (Chironomidae) through the analysis ofsynchronized high speed image sequences from threecameras.Using stereo matching and other computer vision techniques,we are able to reconstruct, in three dimensions, thetrajectories of individual animals within the aggregation.Further analysis of the trajectories should lead to a betterunderstanding of the fundamental interaction rules betweenindividuals.

- Information transfer and behavioural inertia in starling flocks Nature Physics 10 (9), 691-696

- Interaction ruling animal collective behavior depends on topological rather than metric distance: Evidence from a field study Proceedings of the National Academy of Sciences 105 (4), 1232-1237

- Collective Behaviour without Collective Order in Wild Swarms of Midges PloS Computational Biology 10 (7), e1003697

Experiments find coherent information transfer throughbiological groups on length and time scales distinctlybelow those on which asymptotically correcthydrodynamic theories apply.

We need a new continuum theory of collective motion couplingthe velocity and density fields to the inertial spin field recentlyintroduced to describe information propagation in naturalflocks of birds.

- Silent Flocks arXiv:1410.2868

Which is the "recipe" that exactly reproduces the real biological systems? Which are the hypotheses cut by the "Occam's Razor" for which "entities must not be multiplied beyond necessity"?

Biological data have hidden information to be gathered: wehave to solve the "Inverse Problem".We can try to take advantage of the critical aspects ofbiological systems because in physics this is synonymous ofphase transition and scale invariance.A deeper statistical mechanics insight allows us to "rescale"biological data from different eventsand obtain more robust and meaningful answers.It is required a complex and interdisciplinary line of researchthat includes:

- Deep theoretical expertise on statistical physics of complexsystems ;- Bayesian inference on biological data;- Optimization – Simulations - Modeling ;

- Scale-free correlations in starling flocks Proceedings of the National Academy of Sciences 107 (26), 11865-11870

- Statistical mechanics for natural flocks of birds Proceedings of the National Academy of Sciences 109 (13), 4786-4791

Emanuela Zaccarelli

contacts

emanuela.zaccarelli@phys.uniroma1.itOffice: Fermi Building, 106http://glass.phys.uniroma1.it/Emanuela/

keywords

● Simulation and theory of soft matter systems● Gel and glass transitions● Complex effective interactions: novel phases and anomalous dynamics

Complex effective interactions

Colloidal particles can be treated as super-atoms moving in a continuum (solvent) in theframework of statistical mechanics. Theyinteract with effective potentials that can betuned arbitrarily by changing the properties ofthe particle (e.g. shape, architecture,heterogenous surface) or by varying externallythe conditions of the solutions in which theyare suspended. In this way, they experienceinteractions and show phenonema that are notfound in atomic or molecular systems.

The simplest way to control the interactionsbetween colloids is to add smaller particles(cosolute) in the solution, which originate so-called depletion interactions. By tuning theproperties of the co-solutes, novel effects canbe found. For example a co-solute close to itspercolation transition induces so-calledCasimir-like forces on the colloids.

N.Gnan, E. Zaccarelli, F.Sciortino NatureCommunications 5, 3267 (2014)

Gels and Glasses

By tuning effective interactions, we find notonly new thermodynamic phases (e.g. crystalswith unconventional lattice spacings) but alsodifferent types of disordered arrested states: Gels where particles are organized intonetworks and Glasses where particles areblocked by their neighbours.

Recent Results:in collaboration with B. Ruzicka and R.Angelini (CNR) we studied colloidal clays,which form equilibrium gels (Nat. Mater. 10, 562011) and orientational glasses (Nat. Comm.5, 3267 2014);

in collaboration with P. Schurtenberger (Univ.Lund, Sweden), we study microgel polymericparticles, which swell upon increasingtemperature, and can be studied at ultra-highdensities (Soft Matter 9, 3000 2013).

in collaboration with U. Edinburgh and Madridwe study the interplay between crystals andglasses in hard spheres (PNAS 111, 75 2014).