Confirmed Speakers

Thermodynamic properties of water at two extreme thermodynamic conditions were simulated using the latest polarizable models pursuing two main goals: (i) to provide data for regions hardly accessible by experiment, and (ii) to assess the effect of polarizability when comparing the results with those based on pairwise additive models. Concerning supercooled water, in addition to commonly used various order parameters to characterize the structure, and a detailed analysis of the spatial distribution function over the first three coordination shells, we also employed a geometric construction based on the Delaunay tessellation, the method independent of any a priori defined quantity. All these analyses aimed at an examination to what extent qualitative differences in the models (force fields) affect the observed structure. It is found that in most cases the polarizable BK3 model and TIP4P/Ice water yield very similar structural properties. On the contrary, ST2 water exhibits, in majority cases, even qualitatively different properties and these findings are discussed in detail. The obtained results suggest that any conclusion on the behavior of supercooled water based on the ST2 model should be taken, at least, with caution. Thermodynamics of supersaturated (supercooled) steam at conditions occurring in steam turbines, has been studied by a number of theoretical and semi-theoretical methods with the goal to assess available theoretical tools for developing an equation of state. Extended virial expansions with different reference systems have been used along with two, qualitatively different equations of state. It turns out that the perturbed virial expansion with a suitably chosen reference system outperforms other methods, including equations of state originally developed for liquid water.

Jacinta C. Conrad

Department Chemical and Biomolecular Engineering

University of Houston

Dynamics of nanoparticles in complex polymeric fluids

Transport of nanoparticles through complex fluids is essential for environment remediation, nanocomposite processing, and targeted drug delivery. Because nanoparticles are of comparable size to the heterogeneities present in many complex fluids, their dynamics decouple from the bulk fluid properties. Thus, nanoparticles can transport many orders of magnitude faster than expected. To understand the underlying physics of transport in this size regime, we measure the dynamics of nanoparticles moving through polymer solutions, which serve as model complex fluids with well-controlled and tunable heterogeneities. On short time scales, the nanoparticles move subdiffusively through the heterogeneous solutions, coupling to the segmental and center-of-mass dynamics of the polymer coils. On long time scales, the nanoparticle dynamics deviate from Stokes-Einstein predictions and depend on particle size and polymer concentration. Nanoparticle dynamics in polymer solutions are further modified through surface modifications, specifically electrostatic charges or grafted polymers. Electrostatic charges lead to long-range interactions between the particles in organic solvents without disrupting the structure or dynamics of the surrounding polymer solution. The long-range interparticle interactions slow nanoparticle dynamics across the interparticle distance, even though the nanoparticle dynamics are subdiffusive and coupled to the polymer relaxations. Grafted polymers help to stabilize the nanoparticles in complex fluids and lead to soft physical interactions between the grafted particles and the surrounding polymer chains with implications on their transport behavior. Our work illustrates that tuning the nanoparticle size and modifying the particle surface chemistry grants excellent control over the transport properties of nanoparticles through complex media.

Erich A. Müller

Department of Chemical Engineering

Imperial College, London

Effective intermolecular potentials and SAFT equation of state for quantum fluids

Some of the largest technological challenges in the transition to a hydrogen-based society are associated with the transport and storage of hydrogen. Among the many plausible options, the use of liquefied hydrogen (1 bar and 20-30 K) stands out as an economically feasible one. However, the design of process equipment for this purpose requires a very precise knowledge of the thermodynamics of ultra-cryogenic fluids involved such as Hydrogen, Helium, Neon, etc. all of whom present quantum effects at liquid conditions and are ill-described with conventional equations of state or simple force fields. In this talk we will discuss the recent advances in the development of the variable-range Mie version of the Statistical Associating Fluid Theory (SAFT) and in particular, its extensions to quantum fluids via the first and second order Feynman-Hibbs corrections. A new parameter, the de Boer’s quantumness parameter, Λ, is employed to describe the non-conformality of quantum fluids. The proposed theory closely reproduces the macroscopic thermophysical results expected for the underlying potential, hence, consistent with previous versions of the theory, provides for a pathway to link the equation of state to the molecular modelling of the effective two-body potentials. Simulations and theory are presented for pure fluids and mixtures and a discussion on the unusual appearance of solid phases is given.

Gerardo G. Naumis

Depto. De Sistemas Complejos

Instituto de Física, UNAM

Topological map of the Quantum Hall Effect phase diagram and its importance to strained and stacked two-dimensional materials

The discovery of topological phases in superfluids and in the XY model, eventually lead to recognize that in quantum phase transitions there is a role played by topology. In particular, the Hofstadter butterfly is a quantum phase fractal diagram, with a highly complex nested set of gaps, where each gap represents a quantum Hall state whose quantized conductivity is characterized by topological invariants known as the Chern numbers. We will show hoe to determine the Chern numbers at all scales in the butterfly fractal and lay out a very detailed topological map of the quantum phase diagram by using a method used to describe quasicrystals: the cut and projection method. Our study reveals the existence of a set of critical points that separates orderly patterns of both positive and negative Cherns that appear as a fine structure in the butterfly. This fine structure can be understood as a small tilting of the projection subspace in the cut and projection method. These critical points are identified with the Van Hove singularities that exist at every band center in the butterfly landscape. Finally, we show that these results are important to describe strained and stacked two-dimensional materials, as graphene, silicene, dichalcogenides with transition metals, etc. in which complex phase diagrams appear, since strain can be treated as effective pseudomagnetic fields .

Yuri Reyes

Depto. de Recursos de la Tierra

Universidad Autónoma Metropolitana, Lerma

Miniemulsion Polymerization

Dispersed polymer colloids in aqueous media are of great importance from scientific, technological and commercial points of view. A very large amount of these polymer are consumed every year and new materials are continuously obtained by using conventional methods such as emulsion polymerization. However, with this approach it is not easy to obtain hybrid materials with specific morphologies, which can combine the properties of materials of different nature, for example, encapsulated nanoparticles or quantum dots, magnetic nanoparticles, clays, biological molecules, drugs, etc. These new hybrid materials can be obtained by miniemulsion polymerization, that opens the possibilities to synthesize polymer colloids with synergistic properties for a large number of applications. In this talk the advantages and disadvantages of the miniemulsion polymerization, as well as recent developments, will be presented.

Hernán Larralde Ridaura

Instituto de Física, UNAM

On the statistics of texts

Languages have proven to have rather surprising statistical regularities. Amongst these, perhaps the most famous one is Zipf's law, that states that the frequency of a word in a large corpus is proportional to a power of it's rank, which appears to hold for all known languages. Other universal laws are Heap's law, which relates the number of different words in a text with the length of the text; and the degree distribution of the adjacency network, which is again a power law. On a different perspective, hand in hand with these universal properties, different texts frequently “say” different things. And, what is maybe even more surprising, sometimes different texts say the “same thing”. This, of course, is what happens with translations, and, somewhat analogously, with cryptograms. In this talk I will describe our work related to simple mechanisms that give rise to the universal laws of languages, as well as our attempts to identify the signatures of a “text” regardless of the language it is written in.

Victor Romero Rochín

Instituto de Física, UNAM

Global thermodynamics and critical properties of a confined Bose-Einstein condensate

Bose-Einstein condensates and, in general, all ultracold Bose and Fermi gases are experimentally generated in optical and/or magnetic traps that are spatially inhomogeneous. This type of confinement leads, in turn, to a thermalized non-uniform gas. In this talk we shall show that this peculiarity requires that the usual thermodynamics be modified, or “generalized”, to correctly describe those inhomogeneous systems. In particular, the hydrostatic pressure and the volume that the sample occupies are no longer appropriate thermodynamic variables and they must be replaced by a “global” pressure and a “global” volume, proper to each trap. Using these ideas we shall discuss the critical phase transition from a normal gas, confined in a harmonic trap, to a superfluid weakly interacting Bose-Einstein condensate. As part of this study we will introduce an heuristic equation of state that captures the essential critical aspects of the transition.

Ramón Castañeda

Dpto. de Ingeniería Física

Universidad de Guanajuato

Reversible Cluster Formation and Dynamical Arrest in Colloidal Dispersions

Particle aggregation or clustering is an obligatory step for the initiation of the phase separation or the large-scale formation of materials that exhibit a heterogeneous structure, such as gels and porous media. Nevertheless, even though the macroscopic structure of such materials depends on the shape and size of the resulting clusters or aggregates, the cluster formation at equilibrium and its corresponding morphology are not fully understood. The local morphological information is also important for the identification of the physical mechanisms for arrested states of matter, especially gels and glasses, which remains a hotly debated research topic in condensed matter physics. Due to the complex nature and different microscopic details of each particular system, a general, consistent and unified definition is of paramount importance from both scientific and technological viewpoints.

Combining molecular simulations, experimental characterizations and theoretical calculations: 1) we conclusively demonstrate that the cluster morphology in short-ranged attractive colloidal systems (SRACS) at equilibrium conditions can be uniquely determined by the reduced second virial coefficient; our findings link the reversible colloidal aggregation with the extended law of corresponding states, 2) we show that gelation in adhesive hard-sphere dispersions is the result of the rigidity percolation with coordination number equal to 2.4; these results connect the concept of critical gel formation in SRACS to the universal concept of the rigidity percolation and, finally, 3) we provide a unified description and a general overview of the different aspects of the glass transition in largely asymmetric binary mixtures of hard-spheres; we highlight the fundamental relevance in considering explicitly the dynamics of both large and small particles to properly account for the glassy scenario.

Paola Carbone

School of Chemical Engineering and Analytical Science

The University of Manchester

Towards the understanding of the mechanism of ions permeation through graphene-based membranes

Permeation through nanometer pores is important in the design of materials for filtration and separation techniques and because of unusual fundamental behaviour arising at the molecular scale. Membranes comprising or incorporating graphene or graphene oxide (GO) offer remarkable potential for selective uptake and transport of molecular or ionic species. [1, 2] This high selectivity makes these membrane perfect candidates for membrane filtration technology. For a rational design of such nanomaterial the mechanism of permeation through the graphene layers need to be however fully understood and explained. Simulations can help in guiding the design of these extraordinary materials. In this talk we will present some recent results on GO-membrane and the challenges that molecular models face in simulating the real device. [3-5]

References

[1] Nair et al., Science, 2012, 335, 442

[2] Joshi et al., Science, 2014, 343, 6172

[3] Abraham et al., Nat. Nano, 2017, 12, 546

[4] Williams et al., J. Phys. Chem. Lett, 2017, 8, 703

[5] Williams et al, Nanoscale, 2018, 10, 1946

Enrique Hernández-Lemus

Centro de Ciencias de la Complejidad

Instituto Nacional de Medicina Genómica, UNAM

Probabilistic multilayer networks

A wide variety of complex phenomena in the physical, biological and socio-political sciences has become amenable to study, largely due to the progressive abundance of larger, more comprehensive databases. This so-called 'Big Data revolution', has brought the need to develop more powerful analytic approaches and computational techniques that will enable us to understand at a deeper level the intricate relationships that lie within such large data corpora. Here we introduce probabilistic weighted and unweighted multilayer networks as derived from information theoretical correlation measures on large multidimensional datasets. In particular, we will present 'multilayer mutual information networks' as a tensorial extension of Markov Random Fields (MRFs). The joint probability distributions for this class of networks inherit structural properties of MRFs such as having associated Gibbs measures, clique factorization, etc. that will result helpful, both to establish formal connections to statistical physics formalisms and to provide tools for the computational analysis of the underlying systems. We will present the fundamentals of the formal application of probabilistic inference on problems embedded in multilayered environments, as well as a couple of examples taken from the analysis of biological and socio-political systems.

Yvan Castín

Laboratoire Kastler Brossel

École Normale Supérieure

The damping of phonons in a superfluid Fermi gas

The strongly interacting superfluid gases of spin 1/2 fermionic neutral atoms have been studied in the laboratory for about fifteen years. It has recently been possible to prepare them in flat-bottom trapping potentials, rather than in harmonic traps, which will make it possible to study their collective excitation modes, in particular their acoustic (phononic) excitation branch and its attenuation in the superfluid.

From a theoretical point of view, the problem of phonon damping is non-trivial when the acoustic excitation branch is concave. The usual three-phonon damping mechanism of Beliaev-Landau no longer plays, and it is necessary to invoke the effective four-phonon interactions proposed for (bosonic) liquid helium 4 by Landau and Khalatnikov in 1949. Resuming the study of the corresponding damping rate, we arrived at a qualitative disagreement with the results of Landau and Khalatnikov, on the power laws governing damping at low and high wavenumber. We have also analytically calculated the damping rate at the intermediate wave numbers, which, it seems, had never been done.

The Fermi gases admit another branch of excitation, the BCS one, that corresponds to atomic Cooper pair breaking. In practice, as we have shown, at the usual cold atom gas temperatures, the phonon damping by these BCS excitations is not negligible. We calculate it by generalizing to fermions the Landau-Khalatnikov theory of phonon-roton coupling in liquid helium 4. Here again we need to revise the original theory, since some terms in the coupling have been neglected or even omitted.

We will conclude with a discussion of the observability of the predicted damping, in the Fermi gases but also in liquid helium 4.

References

[1] H. Kurkjian, Y. Castin, A. Sinatra, "Landau-Khalatnikov phonon damping in strongly interacting Fermi gases", EPL 116, 40002 (2016).

[2] H. Kurkjian, Y. Castin, A. Sinatra, "Three-phonon and four-phonon interaction processes in a pair-condensed Fermi gas", Annalen der Physik 529, 1600352 (2017).

[3] Y. Castin, A. Sinatra, H. Kurkjian, "Landau phonon-roton theory revisited for superfluid He 4 and Fermi gases", Phys. Rev. Lett. 119, 260402 (2017).

Vanderlei Salvatore Bagnato

Institute of Physics of São Carlos

University of São Paulo

Quantum trapped gas far from equilibrium: turbulence and its properties

The notion of turbulence in the quantum world was conceived long ago, but the occurrence of turbulence in ultracold gases has been studied in the laboratory only very recently. The topic oﬀers new paths and perspectives on the problem of turbulence. The finite size effects create specific characteristics observed. In this presentation we review the general properties of quantum gases at ultralow temperatures paying particular attention to vortices, their dynamics and turbulent behavior. Measurement of the energy spectrum using two techniques will be discussed and related to the present understanding of the theory. Identification of turbulence type based on energy spectrum determination shall be included. Applications of the turbulent cloud, when in expansion, will be discussed. In particular the behavior of matter waves speckle field as well as effective localization during expansion shall be presented. Work supported by FAPESP ( program CEPID) and CNPq ( program INCT).

Kimmo Kaski

Aalto University School of Science, Finland

The Alan Turing Institute, British Library, UK

Wolfson College & CABDyN Complexity Center, Said Business School, Oxford University, UK

Complexity Science Hub Vienna, Austria

Social Physics: Data-Driven and Computational Discoveries of Human Social Connectome

While Information Communication Technology (ICT) has offered us new ways to communicate and socially interact, the usage of which generate digital traces of our individual behaviour as records of ever-growing datasets. The study of such large-scale or Big Data using high-performance computational analysis and modeling with Network Theory approach can give us unprecedented insight into human sociality and to the structures and processes of social life and the society. This is well-demonstrated by our analysis of the dataset of mobile phone communication-logs, confirming the Granovetterian picture for the social network structure, i.e. being modular showing communities with strong internal ties and weaker external ties linking them. More recently the same dataset, but with additional data of the gender and age of the service subscribers, has allowed us to look at the nature of social interaction in more detail and from a different Dunbarian egocentric viewpoint. With this we have got a deeper insight into the gender and age-related social behaviour patterns and dynamics of close human relationships. Our analysis results demonstrate sex differences in the gender-bias of preferred relationships that reflect the way the reproductive investment strategies of both sexes change across their lifespan. We have also investigated the influence of seasonally and geographically related daily dynamics of daylight and ambient temperature on human resting patterns and observed two daily inactivity periods in the population-wide mobile phone calling patterns. The nocturnal resting period was found to be influenced by the length of daylight, and that its seasonal variation depends on the latitude of the phone users. In addition, the duration of the afternoon resting period was found influenced by the temperature, beyond certain threshold value, and that the yearly dynamics of the afternoon and nocturnal resting periods appear to be counterbalancing each other. These empirical findings inspired us to take the next step in network theory, namely developing models to catch some salient features of social networks and processes of human sociality. One of our first models, based on network sociology mechanisms for making friends, turned out to produce many empirically observed Granovetterian features of social networks, like meso-scale community and macro-scale topology formation. The modeling has subsequently been extended to take into account social networks being layered, multiplexing or context based, geography dependent, and having relationships between people changing in time. In sum, the Social Physics’ large-scale data-driven analytics and modelling approaches to social systems opens up an unprecedented perspective to gain understanding of human sociality from individual to societal level, which together with the availability of various socially relevant datasets and development of computational methodologies could eventually lead to tools of social and societal design.

Veronique Trappé

Department of Physics

University of Fribourg

Hallmarks of local intermittent relaxation events in the creep behavior of a colloidal gel

We explore the dynamical and mechanical characteristics of an evolving gel, aiming in particular to assess how the gel evolution impacts the creep response of the system. We find that the creep behavior of the gel is determined by three distinct contributions: an instantaneous elastic, a delayed elastic and a loss contribution. The systematic investigation of these contributions in recovery experiments provides evidence that delayed elastic and loss contributions relate to the same process, namely local intermittent relaxation events that also govern the structural relaxation of the gel at quiescent conditions. Upon increasing the stress towards the yield stress our experimental findings suggest that the size of the restructured zones per event increases, while the rate of intermittent relaxation events remains essentially unchanged.

Carlos A. R. Sá de Melo

School of Physics

Georgia Institute of Technology

Unconventional color superfluidity without quarks:

Ultra-cold fermions in the presence of color-orbit and color-flip fields

We describe how color superfluidity is modified in the presence of color-flip and color-orbit fields in the context of ultracold atoms and discuss connections between this problem and that of color superconductivity in quantum chromodynamics. We study the case of s-wave contact interactions between different colors and we identify several superfluid phases, with five being nodal and one being fully gapped. When our system is described in a mixed-color basis, the superfluid order parameter tensor is characterized by six independent components with explicit momentum dependence induced by color-orbit coupling. The nodal superfluid phases are topological in nature and the low-temperature phase diagram of color-flip field versus interaction parameter exhibits a pentacritical point, where all five nodal color superfluid phases converge. These results are in sharp contrast to the case of zero color-flip and color-orbit fields, where the system has perfect U(3) symmetry and possesses a superfluid phase that is characterized by fully gapped quasiparticle excitations with a single complex order parameter with no momentum dependence and by inert unpaired fermions representing a nonsuperfluid component. In the latter case, just a crossover between a Bardeen-Cooper-Schrieffer and a Bose-Einstein-condensation superfluid occurs. Furthermore, we analyze the order parameter tensor in a total pseudospin basis, investigate its momentum dependence in the singlet, triplet, and quintuplet sectors, and compare the results with the simpler case of spin-1/2 fermions in the presence of spin-flip and spin-orbit fields, where only singlet and triplet channels arise. Finally, we analyze in detail spectroscopic properties of color superfluids in the presence of color-flip and color-orbit fields, such as the quasiparticle excitation spectrum, momentum distribution, and density of states to help characterize all the encountered topological quantum phases, which can be realized in fermionic isotopes of lithium, potassium, and ytterbium atoms with three internal states trapped.

References

[1] D. M. Kurkcuoglu and C. A. R. Sá de Melo, “Color superfluidity of neutral ultracold fermions in the presence of color-flip and color-orbit fields”, Phys. Rev. A. 97,023632 (2018)

[2] D. M. Kurkcuoglu and C. A. R. Sá de Melo, “Creating spin-one fermions in the presence of artificial spin–orbit fields: emergent spinor physics and spectroscopic properties”, J. Low Temp. Phys. 191, 174 (2018).

[3] D. M. Kurkcuoglu and C. A. R. Sá de Melo, “Quantum phases of interacting three-component fermions under the influence of spin-orbit coupling and Zeeman fields”,arXiv:1612.02365v1 (2016).

Charles M. Knobler

Department of Chemistry ad Biochemistry

University of California, Los Angeles

The Effect of RNA Secondary Structure on the in vitro Self-Assembly of Virus-Like Particles

Many viruses consist of an RNA genome that is enclosed in a container called the capsid, which in the simplest cases consists of copies of a single protein. It is remarkable that when molecules of the RNA for CCMV, the Cowpea Chlorotic Mottle Virus, are mixed with the capsid protein in a solution at appropriate conditions of ionic strength and pH, the virus assembles spontaneously into 28-nm diameter icosahedral structures containing precisely 180 copies of the 190-residue capsid protein (CP). Moreover, assembly can occur around other RNAs and other anionic polymers, e.g. polystyrene sulfonate, forming virus-like particles.

Experiments in which two polymers compete for a limited amount of CP allow their relative packaging efficiency to be determined. The studies have probed how packaging efficiency relates to RNA length and, more subtly, to its secondary structure, which in turn depends on the primary sequence. By examining homopolymers such as poly(U) and poly(A) we are able to examine in detail the effects of base stacking and persistence length on packaging efficiency and compare them with theoretical treatments and computer simulations of the assembly process.