| Date |
Speaker |
Affiliation |
Title |
Host |
| September 2nd |
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| September 9th |
Prof. Mark Bowick |
Syracuse University |
Structure and Dynamics in Curvedland |
Middleton |
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| September 16th |
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| Monday, September 19, 11am |
Dr. Olivia White |
MIT |
In Search of Spin Glass Ground States (and why) |
Middleton |
| The term 'spin glass' refers to both experimental systems and theoretical models with enough randomness and frustration to preclude conventional magnetic order. Despite thirty years of study, even the number of ground states in the simplest short-range Ising spin-glass systems is not known. I will introduce the montage phase, a new concrete scenario for a spin glass phase with many states differing by other than symmetry. Of course experimental spin glasses are never near equilibrium on experimental time scales - this is one of their defining characteristics. Nevertheless, their out-of-equilibrium behavior will betray their equilibrium state structure and I will explain why this is so.
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| September 23rd |
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| September 30th |
Prof. Gyorgy Korniss |
Rensselaer Polytechnic Institute |
Synchronization and Transport Efficiency in Small-World Networks |
Middleton |
| Many of our important information and infrastructure systems can be viewed as a complex network with a large number of components, where the links facilitate some form of interaction dynamics or flow between the nodes of the network. We address two problems, solved simultaneosly, in small-world (SW) networks. First, we briefly review the Edwards-Wilkinson (EW) process extended to a SW network. The EW process on a network can be thought of in terms of a synchronization paradigm in a noisy environment. As a linear approximation, it serves as the simplest model for generic causally-constrained queuing networks, such as manufacturing supply chains, e-commerce based services facilitated by interconnected servers, and certain distributed parallel schemes on computer networks. In the context of the latter, we have shown that when extending the original short-range connections to a SW-like network (essentially, by adding a small density of random links on top of a regular graph), the spread between completion times of tasks performed on different nodes of a computer network remains bounded, rather than diverging over time. Further, an infinitesimal extra "cost" is sufficient to achieve this reduction. An important measure of efficiency is the spread (or "width") of task-completion landscapes in such processing networks (larger spread corresponds to longer delays and poorer efficiency). It becomes evident that this measure---the width of the EW landscape on a network---is identical to the average resistance (characterizing transport efficiency) of the same network. This connection between the average spread of an EW steady-state landscape and the resistance of the same network gives some insight in treating synchronization and transport efficiency on the same footing (on any network). In particular, we obtain the scaling properties of the effective system resistance for small-world networks.http://www.rpi.edu/~korniss/Research/ |
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| October 7th |
Dr. Igor Kulic |
University of Pennsylvania |
Physics of Biological and Biomimetic Nanomotors |
Schwarz |
| |
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| October 14th |
Prof. Yan-Yeung Luk |
Syracuse University |
Cell Adhesion on Gradient Nanotopography & Useful Phase Behaviors of Novel Biocompatible Liquid Crystals |
Middleton |
| |
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| October 21st |
Prof. Thomas Vojta |
University of Missouri-Rolla |
Quantum Phase Transitions and Disorder: Infinite Randomness,
Quantum-Griffiths Singularities, and Smearing. |
Marchetti |
| Quantum phase transitions are transitions occurring at zero temperature
as a function of a parameter like pressure, chemical composition or
magnetic field. In recent years, they have become one of the central
paradigms in condensed matter physics, and they are believed to underlie
a number of exciting low-temperature phenomena like exotic superconductivity
and non-Fermi liquid behavior. At quantum phase transitions, impurities
and other forms of quenched disorder can have very peculiar and surprisingly
strong effects: In many random quantum Ising magnets the critical point is
of infinite-randomness type, i.e., counter-intuitively, the disorder strength
increases without limit under coarse graining. This gives rise to activated
exponential scaling rather than the usual power-law scaling. In addition,
rare disorder fluctuations lead to strong thermodynamic singularities, called
the quantum-Griffiths singularities, in the vicinity of the actual transition.
In metallic systems the effects of these rare fluctuations can be
even stronger,
leading to a destruction of the phase transition by smearing.
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|
| Monday, October 24, 11am |
Prof. Mike Moore |
University of Manchester, UK |
What is the order parameter of spin glasses? |
Middleton |
| |
| October 28th |
Prof. Ari Mizel |
Pennsylvania State University, University Park |
Quantumness of a Qubit |
Plourde |
| With the recent surge of interest in quantum computation, it has
become very important to develop clear experimental tests for
'quantum behavior' in a system. This issue has been addressed in
the past in the form of the inequalities due to Bell and those due to
Leggett and Garg. These inequalities concern the results of ideal
projective measurements, however, which are experimentally difficult
to perform in many proposed qubit designs, especially in many solid
state qubit systems. Here, we show that weak continuous measurements,
which are often practical to implement experimentally, can yield
particularly clear signatures of quantum coherence.
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|
| November 4th |
Prof. Murugappan Muthukumar |
University of Massachusetts, Amherst |
How DNA worms through protein channels |
Movileanu |
| When polymer molecules are forced to navigate through narrow channels, their dynamics and transport are controlled by entropic barriers. Using entropic barrier theory for polymer dynamics, we have developed a model for polymer translocation through synthetic pores and protein channels. The predictions of our theory and accompanying simulations will be compared with the recent electrophysiology experiments on single DNA molecules. A discussion of these issues and their significant impact on strategies for DNA-sequencing and efficient separation protocols for charged polymers will be presented. |
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| November 11th |
Prof. Salvatore Torquato |
Princeton University |
Optimal Particle Packings: Problems for the Ages |
Bowick |
| Packing problems, such as how densely solid objects fill space, have fascinated people since the dawn of civilization, and continue to intrigue scientists because of their connection to a host of problems that arise in the physical sciences, mathematics and biology. Particle packings have been studied to understand the structure and bulk properties of living cells, liquids, composites, granular media, glasses and crystals. Sphere packings in high dimensions have relevance in communications theory. There are many open questions. What are the best packings of spheres in dimension greater than 3? What are the densest packings of nonspherical objects in 2 and 3 dimensions? Can random packings ever fill space more densely than ordered packings? Can "randomness" be quantified in a meaningful and precise manner? Can the rigorous study of the hard-sphere model shed light on disorder/order phase transitions? Two recent concepts,"jamming" and "order metrics", facilitate the characterization of optimal packings. The former is related to the mechanical stability of the packing and the latter describes the degree of randomness of the packing via scalar order metrics. Besides the maximal density FCC point for sphere packings, I will discuss other interesting optimal points, including the "maximally random jammed" state, which replaces the venerable but ill-defined "random close packed" state, as well as the jammed state with the smallest density. Recently, we have shown that ellipsoids can randomly pack more densely than spheres. This work has implications for the existence of a thermodynamically stable glass. Moreover, we have discovered a family of crystal ellipsoid packings with the highest known density. Finally, we have devised a new provisional lower bound on the maximal density of sphere packings in arbitrary dimension, which provides the first putative exponential improvement on the 100-year-old lower bound due to Minkowski. |
|
| November 18th |
Prof. Randall Kamien |
University of Pennsylvania |
Bending the Rules |
Kung |
| Though the plethora of smectic liquid crystalline phases requires a complex and arcane taxonomic system, the variety comes from the different ways of stacking the mesogens from plane to plane. Until the discovery of layered systems with long- range cubic order, also known as smectic blue phases, there has been little attention devoted to three dimensional, space-filling, layered structures. Motivated by the discovery of both smectic blue phases and the structure of the B4 phases of bow-shaped mesogens, I will discuss the theory of smectic order based on non-planar geometries appealing to results in topology and geometry.
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|
| Monday, November 21, 11am |
Prof. A. R. Bausch |
Technische Universitat Munchen |
Physics of complex actin networks: from molecules to networks |
Bowick |
| The cytoskeleton, a dynamic network of semiflexible actin filaments and associated regulatory proteins, is responsible for the extraordinary viscoelastic properties of cells. In order to understand the underlying physical principles it is important to determine in vitro the mechanical properties of entangled, cross linked and active actin networks on a microscopic scale. Besides the specific interactions in cells, unspecific physical interactions also drastically change the viscoelastic response of the cytoskeletal networks. Here we address the important aspects of geometrical confinement and relate the molecular structure of genetically designed crosslinker molecules to the structural and rheological properties of actin networks.
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| November 25th |
Thanksgiving |
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| December 2nd |
|
Syracuse University |
NY Complex Matter Workshop |
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| Tuesday, December 6, 4pm |
Prof. Pierre Le Doussal |
Laboratoire de Physique Theorique de l'Ecole Normale Superieure |
Functional RG for pinned random
systems: tests and recent applications |
Middleton |
| I'll review recent progress in RG applied
to glass phases of elastic objects in
quenched disorder. Remaining issues
will be discussed and tests proposed.
If time permits, recent applications to
contact line depinning, random field
transitions and chaos will be presented.
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| December 9th |
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| Date |
Speaker |
Affiliation |
Title |
Host |
| January 20th |
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| Monday, January 23, 11am |
Jung-Ren Huang |
University of Chicago |
Theory of Myelin Formation and Coiling: A Simple Answer to a Century-old Puzzle |
CMT |
| The formation and coiling of myelins has been a mystery since their discovery in 1854. Inspired by a novel experiment done at the University of Chicago, I will explain why myelins form using a geometric argument: the bilayer repeat spacing increases and thus the repulsion between bilayers decreases when a multilamellar disk is converted into a myelin without gain or loss of material and with number of bilayers unchanged. Sufficient reduction in bilayer repulsion can compensate for the cost in curvature energy, leading to a net stability of the myelin structure. A numerical estimate predicts the degree of dehydration required to favor myelin structures over flat lamellae. In addition, I will propose a model to explain coiling of myelins composed of fluid bilayers. This model allows the constituent bilayer cylinders of a myelin to be non-coaxial and the bilayer lateral tension to vary from bilayer to bilayer. The analysis of a simple two-bilayer case suggests that a bilayer lateral tension of about 1 dyne per cm can easily induce coiling of myelins of typical lipid bilayers. From a mechanical point of view, the proposed coiling mechanism is analogous to the classical Euler buckling of a thin elastic rod under axial compression. This model signifies the importance of bilayer lateral tension in determining the morphology of myelinic structures.
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| January 27th |
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| Monday, January 30, 11am |
Claudio Castelnovo |
Boston University |
Glassiness in Classical and Quantum Systems Subjected to Hard Constraints |
CMT |
| In this talk, I will illustrate how glassiness can emerge in a two-dimensional homogeneous system without disorder, when the local degrees of freedom are subjected to a strong constraint, and the system is coupled to a bath. I will begin discussing a classical constrained Ising model that exhibits a dynamical obstruction to its ferromagnetic transition, and it undergoes a freezing `transition' (below T_c) into a non-magnetized, fully-polycrystallized phase. I will then discuss how the physics of this system is affected when quantum mechanics is brought into the picture, via a transverse-field coupling to a local thermal bath (a la Caldeira-Leggett). In particular, I will show that the relaxation time needed for a generic initial state to decay to the ground state in some region of parameter space diverges exponentially with the system size, a property that signals quantum glassiness. |
|
| February 3rd |
Prof. Tewodros Asefa |
Syracuse University |
Multifunctional Nanostructured Materials: From Synthesis to Potential Applications |
Schiff |
| |
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| Tuesday, February 7, 11am |
Aparna Baskaran |
University of Florida, Gainesville |
Statistical Mechanics and Hydrodynamics of a Granular Fluid |
CMT |
| Granular materials are ubiquitous in nature and industry. When these materials undergo rapid collisional flow, they exhibit fluid like behavior. In this talk, the key ideas that go into a hydrodynamic description of these fluidized states in terms of its number density, flow velocity and granular temperature are discussed. Next, the statistical mechanics of a model system consisting of N smooth hard particles is formulated and used to carry out a Linear Response analysis that identifies exact expressions for the transport coefficients in the hydrodynamic equations associated with this fluid, in terms of time correlation functions over a reference homogeneous ensemble. These are the analogues of the Helfand and Green - Kubo expressions that have been derived for normal fluids. Some comments are made on the content of these expressions and their implication for energy and momentum transport in a granular fluid.
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|
| Thursday, February 9, 4pm |
Noah Bray-Ali |
University of California, Berkeley |
Ordering near the percolation threshold in models of interacting bosons with quenched dilution |
CMT |
| Randomly diluted quantum boson and spin models in two dimensions combine the physics of classical percolation with the dimensionality dependence of ordering in quantum models. This combination is rather subtle for the percolation cluster near threshold, because it has fractal dimension between one and two. Two experimentally relevant examples are quantum rotors and Heisenberg antiferromagnets. This seminar follows two related approaches to quantum rotors. In the first, we expand away from the classical phase and see that it is stable to small fluctuations. In the second, we focus on the quantum rotors living on a certain, quasi-one-dimensional sub-lattice of the percolation cluster, and see that the simple geometry allows us to make asymptotically exact statements even if the rotors fluctuate strongly. The talk closes with some comments on recent numerical and experimental evidence that magnetic order persists at percolation threshold in a quantum antiferromagnet.
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| February 10th |
Dr. Christian Santangelo |
University of Pennsylvania |
Taming competing length scales in electrostatics and self-assembly |
Schwarz |
| Complex fluids differ from simple fluids by the wealth of phenomena they are able to exhibit. This complex behavior can emerge from the interplay between physics on different length scales. As one example of this, the short-distance correlations between ions has been implicated in several nonintuitive phenomena, including the bundling of like-charged molecules. I will discuss my recent work constructing a coarse-grained model for charged systems that also accounts for these short-distance ionic correlations. A number of physically appealing conclusions emerge naturally from this framework, allowing a description of the behavior of ions both near and far from highly charged surfaces. I will also describe a system of particles with isotropic, repulsive interactions on two length scales that exhibits an extremely rich phase diagram. In two dimensions, this includes cluster, striped, and inverse micellar phases reminiscent of other self-assembling systems with more complicated (and attractive) interactions. I will extend my method to study the morphology of this repulsive self-assembly.
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| February 17th |
Pavel Kraikivski |
Max Planck Institute of Colloids and Interfaces, Potsdam, Germany |
Polymer manipulation and motility on substrates |
CMT |
| Two subjects related to the non-equilibrium dynamics of polymers or biological filaments adsorbed to two-dimensional substrates will be discussed.
The first part is dedicated to thermally activated dynamics of polymers on structured substrates in the presence or absence of a driving force. The structured substrate is represented by double-well or periodic potentials.
Both homogeneous and point driving forces are considered. Point-like driving forces can be realized in single molecule manipulation by atomic force microscopy tips. Uniform driving forces can be generated by hydrodynamic flow or by electric fields for charged polymers.
The second part is dedicated to collective filament motion in motility
assays for motor proteins, where filaments glide over a motor-coated
substrate. The model for the simulation of the filament dynamics
contains interactive deformable filaments that move under the influence of
forces from molecular motors and thermal noise. Motor tails are attached
to the substrate and modeled as flexible polymers (entropic springs),
motor heads perform a directed walk with a given force-velocity relation.
I will consider the collective filament dynamics and pattern formation as
a function of the motor and filament density, the force-velocity
characteristics, the detachment rate of motor proteins and the filament
interaction. In particular, the formation and statistics of filament
patterns such as nematic ordering due to motor activity or clusters due to
blocking effects are investigated.
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| February 24th |
Prof. Paul Goldbart |
Univeristy of Illinois, Urbana-Champaign |
Superconducting Quantum Interference Devices at the Nanoscale
|
Xing |
| SQUIDs, and other superconducting devices, can now be fabricated at the nanoscale by depositing suitable metals on to individual molecules, such as DNA and carbon nanotubes [1]. In this colloquium I shall describe how these nanoscale superconducting devices are made and how they operate. I shall pay particular attention to the intrinsic electrical resistance of these devices, especially their sensitivity to magnetic fields. This particular feature hints at possible uses of nanoscale SQUIDs, such as for mapping the phase of the superconducting order parameter and testing for superconducting correlations in novel materials and settings. As we shall see, simple models, rooted in the classic approaches to electrical resistance in Josephson junctions and superconducting wires, are capable of providing a quantitative understanding of the properties of nanoscale SQUIDs [2].
[1] D.S. Hopkins, D. Pekker, P.M. Goldbart and A. Bezryadin, Quantum interference device made by DNA templating of superconducting nanowires, Science 308, 1762-65 (2005).
[2] D. Pekker, A. Bezryadin, D.S. Hopkins and P.M. Goldbart. Operation of a superconducting nanowire quantum interference device with mesoscopic leads, Physical Review B 72, 104517 (2005).
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| March 3rd |
TBA |
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TBA |
CMT |
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| March 10th |
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| March 17th |
Spring Break/APS March Meeting |
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| Tuesday, March 21, 11am |
Prof. Monwhea Jeng |
Southern Illinois University |
Glassiness in Classical and Quantum Systems Subjected to Hard Constraints |
Schwarz |
| The Abelian sandpile model, introduced by Bak, Tang and Wisenfeld in 1987, is the prototypical modelof self-organized criticality. It is a simple cellular automata that evolves naturally to a critical point, with power law correlations and self-similar structures, without any fine-tuning of parameters. This model is interesting not just as a model of self-organized criticality, but because it can be shown to be equivalent to the central charge -2 logarithmic conformal field theory. The structure of logarithmic conformal field theories is not well understood, but understanding the structure is of crucial importance, since critical phenomena in two dimensions with quenched disorder are naturally logarithmic conformal field theories. We find the field identifications of the weakly allowed cluster variables and higher height variables in the sandpile model, both in the bulk, and along open and closed boundaries. These identifications give a complete picture of the behavior of the height variables in the sandpile model, and in particular, show that in the bulk the higher heights correspond to the logarithmic partner of the height one variable.
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| March 24th |
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| March 31st |
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| April 7th |
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| April 14th |
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| April 21st |
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| Monday, April 24, 11am |
Prof. Guy Adriaenssens |
Katholieke Universiteit Leuven |
Optoelectronic characterisation of defects in amorphous chalcogenides |
Schiff |
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| Tuesday, April 25, 11am |
Dr. Mouneim Ettouhami |
University of Toronto |
Entanglement in flux-line liquids |
Xing |
| A distinctive feature of vortices in high temperature superconductors is that they form a liquid phase--rather than an ordered Abrikosov lattice--over a substantial region of the magnetic field B-temperature T phase diagram of these materials. In this talk, I will first review the early theoretical approaches to flux-line liquids--mainly boson mapping hydrodynamic treatments and numerical simulations, which have focused
on density correlations and predicted a heavily entangled flux-line liquid. Going beyond these early treatments, I will discuss a microscopic mean field theory of dilute flux-line liquids which gives access not only to density correlations but to correlations between individual vortex conformation variables as well. Within this approach, I will argue that interactions between vortices produce a term in the Hamiltonian of the internal modes of the flux lines which confines their transverse fluctuations. This suggests the existence of a weakly entangled state, where the average width of flux lines can be larger than the average distance between the lines without diverging with the sample thickness L. In presence of disorder, I will show how a dynamical version of our model can be used to derive the long scale, coarse-grained equation of motion of the driven flux liquid, which apart from new Kardar-Parisi-Zhang non-linearities, has the same analytic form as the equation of motion for unpinned vortices, with disorder-renormalized coefficients. Consequences on our understanding of experiments on flux line liquids will be briefly discussed.
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| April 28th |
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| May 5th |
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| Wednesday, May 10, 11am |
Dr. Serguei Brazovski |
University of Paris-Sud |
Ferroelectricity and Charge order in Organic conductors:
Access to Physics of Solitons |
Marchetti |
| The family of best known molecular conductors TMTTF/TMTSF-X (Bechgaard-Fabre salts) demonstrates almost all known electronic phases in parallel with a set of weak structural transitions and some mysterious structureless ones. Recently, their nature became elucidated by discoveries of a huge ferroelectric anomaly and by the NMR evidences for the charge disproportionation. The observations have been interpreted as the never expected Ferroelectric transition. The phenomenon unifies a variety of different concepts and observations in quite unusual aspects or conjunctions: ferroelectricity of good conductors, structural instability towards the Mott-Hubbard state, Wigner crystallization in a dense electronic system, ordered 4K_F density wave, richness of physics of solitons, the interplay of structural and electronic symmetries. The state gives rise to three types of solitons: pi- solitons (holons) are observed in conductivity and optics; fractionally charged solitons are seen as ferroelectric domain walls via the frequency dispersion of the electric response; topologically coupled combined spin-charge solitons appear below occasional subsequent structural transitions.
REFERENCES:cond-mat/0012237/0304076/0304483/0306006 |
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| May 12th |
Dr. Olivia White |
MIT |
Trading space for time: a model of a mechanism for short-term memory |
Middleton |
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| Monday, May 15, 11am |
Dr. Nicholas Darnton |
Harvard University |
Coherent motion in bacterial swarms |
Trodden |
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Condensed Matter & Biological Physics Seminar