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2020-12-10

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Biology Seminar by Dr. Euki Yazaki on December 10, 2020

In iTHEMS Biology Seminar on December 10th, Dr. Euki Yazaki (iTHEMS) talked about recent techniques and problems in obtaining the large-scale sequence data of eukaryotes. He first mentioned the importance of identifying and comparing the genome sequence in biology. Then, he illustrated the two representative sequencing methods, Sanger sequencing and next-generation sequencing (NGS). He clearly explained the features of these methods, highlighting the advantages of NGS in exploring large-scale or novel sequences. In the latter part, he introduced a method using the graph theory to reconstruct the large-scale genome data from the fragments of a sequence obtained by NGS. He lastly pointed out some problems in the current reconstruction method, and we discussed possible ideas to mitigate them after the talk. We are grateful to Euki for the stimulating talk! Kyosuke Adachi (BDR/iTHEMS)

2020-12-09

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Math Seminar by Dr. Tianfeng Hou on November 13, 2020

On November 13, Tianfeng Hou, a new member of the team, gave a math seminar on the Monte Carlo study. In the first part, the speaker focuses on quasi-Monte Carlo method and its probabilistic assessments. In the second part, the speaker explained reduced-order models and how they work in the hygrothermal model. He first showed his model works efficiently in the linear scenario. On the other hand, he explained that his model is not so efficient in some nonlinear scenario.

2020-12-08

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Information Theory SG by Dr. Akinori Tanaka on December 8, 2020 (Continuation of last week)

Continued from last week, Dr. Akinori Tanaka (Senior Research Scientist of iTHEMS and AIP) gave us a talk about the connection between the thermodynamic law and the algorithms of deep learning. He first reviewed the second law of thermodynamics in Langevin systems and the representation of stochastic gradient descent algorithms using Gaussian fluctuation. He then explained about Generative Adversarial Networks (GAN), which can be used in producing near realistic fake images. Based on mathematical correspondence, he discussed a possible application of the modified thermodynamic law to the algorithms of GAN. We are thankful to him for the exciting talk! Kyosuke Adachi (BDR/iTHEMS)

2020-12-07

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First Information Theory SG by Dr. Akinori Tanaka on December 1, 2020

Kicking off the study group of information theory, Akinori Tanaka (Senior Research Scientist of iTHEMS and AIP) talked about the connection between Langevin equation and deep neural networks. He first showed that by analyzing Langevin equations one can derive the second law of thermodynamics which posits that the total entropy of the system should increase. He then delved into stochastic gradient descent (SDG) and showed how to apply it to train the neural network in general. We discussed too enthusiastically for him to finish his talk, and so we'll organize the second part next week (08 December 2020). We are all looking forward to discussing more, and thank you so much for the elegant talk! -Ryosuke Iritani (iTHEMS)

2020-12-07

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Math Seminar by Dr. Martin Skrodzki on November 30, 2020

Our colleague Martin Skrodzki gave a farewell-talk in iTHEMS Math seminar on November 30. The title of the talk was “Flat and spherical surface approximations”. He talked about two approaches to approximate surfaces by using flat objects and spherical objects. In the first part, he explained the approximation using flat objects. Naively, there are two approaches to approximate surfaces. One is local and the other is global. In local approach, we need to get extremely many samples. In global approach, it will produce extreme torsion of surfaces. To remedy these problems, we should think of medium approach, i.e., patching of small simple flat objects (like covering of manifolds). This is called Variational Shape Approximation (VSA). The VSA has three steps: seeding, flooding and updating (and we iterate these recursively). This method gives us a very nice approximation of surfaces, but it still has some defects. Indeed, The recursive process does not always converge, the result depends on initial random choice of seeding, and it also depends on the artificial choice of the number of proxies we use. Therefore, Martin and his collaborators refined the VSA, by adding new steps called “splitting”, “Merging” and “Switching”. These steps avoids all defects above. In the second part, he explained his project on approximating surfaces using spheres. He shows some extreme examples of surfaces which are not relevant for spherical approximation: cone and toilet paper. If you imagine a needle-shaped cone, then its intersection with a ball will be very small. On the other hand, if you thing of rolled paper, then its intersection with a ball have too large area. However, if the surface we want to approximate satisfies a relevant condition, we can obtain a condition on the radius of the ball we use to approximate the surface. During the lecture, he proposed an interesting question on the maximum/minimal area of the intersection of the ball and the surface, and there was an exciting discussion including the audience.

2020-12-07

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DMWG seinar by Dr. Naka: Directional Direct Detection Experiments

Among the kinds of dark matter (DM) candidates, Weakly Interacting Massive Particle (WIMP) shows a strong model motivation. It achieves the current DM density naturally via the so-called thermal freeze-out mechanism. The strength of the interaction between WIMP and the standard model particles should be finite, and various direct detection experiments have already excluded a large part of the favored parameter space. We are now in the phase to consider the next strategy. There are several directions to proceed. For example, annual and/or diurnal modulation of the event rate of the DM-nucleon scattering. However, the expected modulation amplitude is so small that a few percent for annual modulation and less than 1% for the diurnal case. Kinds of on-going experiments intensively search the modulation signature now, however, it is still difficult to confirm. Another possibility is to make use of directional information. One important advantage of the directional search is its power for background rejection. The DM signal should be more frequently found in the direction corresponding to the Galactic Center while the backgrounds are in different directional distributions. These differences enable us to reduce the number of scattering events required for claiming the detection from O(1e4) to O(100), compared to the conventional direct detection cases. Furthermore, it could potentially provide us with information about the velocity distribution function, of which precise understanding is a key to any kinds of direct detection experiments, as well as the scenarios explaining the evolution of our Galaxy. Hence, the directional search is an attractive idea to probe the nature of DM. Recently, such projects are launched, and still some technical issues to solve remain. We have to achieve the O(1e-9)m scale resolution of the particle track, to confirm the scalability and stability, and to understand the ultra-low background. Many projects are now tackling these problems. The new era for direct DM search now begins!

2020-11-30

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Biology Seminar by Dr. Hidenori Tanaka on November 20, 2020

In iTHEMS Biology Seminar on November 20th, Dr. Hidenori Tanaka (Physics & Informatics Laboratories, NTT Research) gave us an exciting talk about physics principles in neural networks. He first reviewed the basic scheme of deep learning using neural networks. Then, he presented three questions regarding both neural science and machine learning and explained his recent works which address these questions. He stressed how physics principles like symmetry and conservation laws are useful in extracting minimal features of biological circuit models, improving algorithms to simplify neural networks, and predicting learning dynamics of neural networks. As his talk was clear and kind to both specialists and non-specialists, there were various questions from the audience. Hidenori is a very active researcher, and I was happy to invite him as a guest speaker. Kyosuke Adachi (BDR/iTHEMS)

2020-11-24

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Math Seminar by Dr. Takahiro Kitayama on November 16, 2020

On November 16, professor Takahiro Kitayama from University of Tokyo gave a talk entitled “Representations of fundamental groups and 3-manifold topology” at the iTHEMS math seminar. In the first part, he introduced a central motivation of 3-manifold topology: classify all 3-manifolds up to diffeomorphisms. As one of the important tools, he introduced the fundamental groups of spaces. He reviewed several known results of the fundamental groups of manifolds. Next, he focused on essential surfaces and introduced Haken 3-manifolds as an important class of 3-manifolds. In particular, he introduced several examples of Haken and non-Haken manifolds. At the end of the first talk, he explained SL(2,C)-representation spaces (character varieties) of the fundamental groups of 3-manifolds. He mentioned that the representation space has been used as a fundamental tool to classify knots and 3-manifolds. In the second part, he first mentioned Culler-Shalen, Morgan-Shalen’s theorem which says that an ideal point of the SL(2,C)-character variety of a given 3-manifold M gives an essential surface of M. Friedl, Hara, Kitayama, and Nagel developed C-S and M-S’s theory for the Lie group SL(n,C). He explained the main idea to obtain all essential surfaces from ideal points of SL(n,C)-character variety. In particular, he introduced the tautological representation depending on some affine curve of the SL(2,C)-character variety, and an action of the fundamental group on some contractible simplicial complex called the Bruhat-Tits building. Then by a standard argument of topology, he constructed some simplicial map f from the universal covering space of a given 3-manifold to the Bruhat-Tits building. By taking the inverse image of f(after ignoring trivial parts and dividing by the fundamental group of the 3-manifold), he finally constructed an essential surface. Next, he also told us about a relation between (homotopy types of) boundary loops of essential surfaces of knot complements and slopes of sides of the Newton polygon obtained from A-polynomials. He said an essential idea of the result, which can detect whether the boundary of an essential surface obtained from an ideal point is boundary parallel or not. At the end of the second talk, as the leading coefficients of torsion functions, he gave a function c_{M, ψ} on the SL(n, C)-character variety. After explaining Dunfield-Friedl-Jackson’s conjecture, he gave a partial solution of the conjecture which is related to the finiteness of c_{M, ψ} on the ideal points.

2020-11-16

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Math-Phys joint Seminar by Dr. Naoto Shiraishi on November 10, 2020

On November 10, Dr. Naoto Shiraishi from Gakushuin University gave a talk entitled “Mathematics of thermalization in isolated quantum systems” at the iTHEMS Math-Phys joint seminar. In the first part, he reviewed some results and problems of quantum thermalization. Besides, he explained the typicality of equilibrium states, the relaxation caused by large effective dimensions, and the weak/strong eigenstate thermalization hypothesis mathematically. In the second part, the speaker discussed the difficulty of the thermalization problems and some of his results. Mainly, he showed the absence of local conserved quantities in the S=1/2 XYZ chain with a magnetic field. The talk had many participants from in and out iTHEMS and many stimulating discussions.

2020-11-09

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Biology Seminar by Dr. Takahiro Sakamoto on November 5, 2020

On November 5th, Takahiro Sakamoto from SOKENDAI gave a talk at the iTHEMS Biology Seminar. First, he gave a very nice introduction about the basics of population genetics, and then, he talked about his theoretical study about how genetic divergence proceeds when there is migration between two locally adapted sub-populations. He did very well in explaining his research, which is actually quite complicated, to non-experts, and because of that there were many questions and fruitful discussions. Takahiro is a student from my previous lab and I had in mind to invite him at some point because I knew he is good at giving talks and that his research should be interesting to iTHEMS people. So I was pleasantly surprised that Okada-san invited him, and I was very glad to see that many people enjoyed his talk. Jeffrey Fawcett

2020-11-09

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Biology Seminar by Dr. Jeffrey Fawcett on October 29, 2020

In iTHEMS biology seminar on October 29, Jeffery Fawcett (RIKEN iTHEMS) gave us a talk on genomic data analysis. He started from explaining basic concepts of evolution and explained a couple of important quantities in population genetics, such as nucleotide diversity and the site frequency spectrum, which can be used to infer an underlying evolutionary process from sampled DNA sequences. He also explained statistical methods to study population structures and illustrated one of the methods in a study of the history of Japanese populations, which was very interesting. He made a great effort into his presentation. His talk was very educational and informative, and both experts and non-experts enjoyed his talk. Besides, the next biology seminar on 11/5 was on theoretical population genetics (I was actually the host), and Jeff helped us to prepare for the next week's seminar. Thank you very much, Jeff! - Takashi Okada

2020-10-30

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iTHEMS Theoretical Physics Seminar on October 23, 2020

The iTHEMS Theoretical Physics Seminar is held on October 23, 2020. The speaker is Dr. Masanori Hanada in Department of Mathematics, the University of Surrey. The title is ”Toward simulating Superstring/M-theory on a Quantum Computer”. He present a framework for simulating superstring/M-theory on a quantum computer, based on holographic duality. Because holographicduality maps superstring/M-theory to quantum field theories (QFTs), we can study superstring/M-theory if we can put such QFTs on a quantum computer --- but it still looks like a complicated problem, if we use a usual lattice regularization. Here he propose an alternative approach, which turns out to be rather simple: we map the QFT problems to matrix models, especially the supersymmetric matrix models such as the Berenstein-Maldacena-Nastase (BMN) matrix model. Supersymmetric matrix models have natural applications to superstring/M-theory and gravitational physics, in an appropriate limit of parameters. Furthermore, for certain states in the Berenstein-Maldacena-Nastase (BMN) matrix model, several supersymmetric quantum field theories dual to superstring/M-theory can be realized on a quantum device. It is straightforward to put the matrix models on a quantum computer, because they are just quantum mechanics of matrices, and the construction of QFTs is mapped to the preparation of certain states. He show the procedures are conceptually rather simple and efficient quantum algorithms can be applied. In addition, as a (kind of) byproduct, he provide a new formulation of pure Yang-Mills on quantum computer. The seminar was held via the Zoom online conference systems, and more than 15 people including outside of iTHEMS attended the seminar.

2020-10-23

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iTHEMS Theoretical Physics Seminar by Dr. Tokuro Fukui on October 22, 2020

On October 22, the iTHEMS-phys seminar entitled "Realistic shell model and chiral three-body force” given by Dr. Tokuro Fukui (YITP, Kyoto U.) was held. He and his collaborators proposed the way to calculate matrix elements of the three-body nuclear force, and showed the importance and effects of the three-body nuclear force in medium-heavy nuclei, such as calcium and nickel isotopes, starting from the chiral nuclear force using the shell model calculation. During his seminar, he introduced their works from the introduction to state-of-art results. The seminar was held via the Zoom online conference systems, and more than 25 people including outside of iTHEMS attended the seminar.

2020-10-22

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Biology Seminar by Dr. Christos Merkatas on October 21, 2020

On October 21st, Dr. Christos Merkatas from Aalto University in Finland gave a talk at the iTHEMS Biology Seminar. His talk was entitled, “Bayesian Nonparametric Estimation of Random Dynamical Systems”. Suppose that the observed time series is small, and the noise process is non-Gaussian. How can we reconstruct and predict the behavior of the system? Dr. Merkatas showed that the proposed Bayesian approach enables us to reconstruct and predict the system by inferring the number of unknown components and their variances. According to him, the method can be applied to the problems in physics, biology, and economy. Since some of the audiences including me were not familiar with his method, we asked many basic questions. The talk by Dr. Merkatas was great and also educative. Gen Kurosawa

2020-10-21

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DMWG seminar by Dr. Rinaldi: Towards the cosmological signature of composite DM

There are lots of dark matter (DM) candidates of particles and/or non-particles. One important requirement is that DM should be massive. When we consider the main origin of the visible mass in the Universe, it is the proton, i.e. a composite of three-quarks bound by the strong interaction. Then we can realize the DM mass naturally if we introduce similar dynamics in the dark sector. The interaction between the dark and the standard model sector is different from that of DM self-interaction, hence it is also safe under the cosmological requirements. Among the varieties of composite DM models, the stealth DM scenario is a well-motivated one with minimal assumptions. It is different from other baryonic composite DM since it is developed for solving the problem of DM rather than for another mystery in the standard model. Let's consider the signatures in cosmological observations which we could expect for the stealth DM scenario. Since the structure of the stealth DM is similar to that of the standard model baryons, they should experience the confined-unconfined phase transition in the early Universe. If the phase transition is of the 1st order, numerous vacuum babbles are produced in the transition from the false- to the true vacuum. The collision of these bubbles sources the low-frequency gravitational waves (GWs) of a ~nHz-mHz range. However, it is difficult to calculate the physics around the phase transition. Indeed, it is not obvious whether the phase transition occurs in the 1st order or not. When it is of the 1st order, the gravitational wave spectrum is determined using the temperature of the Universe at the phase transition. Dr. Rinaldi and the members of the Lattice Strong Dynamics collaboration have investigated the phase transition in the stealth DM scenario by applying the sophisticated calculation techniques developed for the strongly-interacting sector in the standard model. They reveal that the lower bound of the 1st order phase transition temperature for the scenario, which is then directly converted to the lower bound on the frequency of the GW. The technique should enable us to study DM from multiple aspects as is shown in this talk. Furthermore, this is the beginning of a new interdisciplinary study in which DM becomes the portal to connect the strong dynamics and GW cosmology, which could further enhance our understanding of this world!

2020-10-07

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Math-Phys Joint Seminar by Toshihiro Ota on October 2, 2020

On October 2, Toshihiro Ota gave a talk at the iTHEMS Math-Phys Joint Seminar. His whole talk was on the interrelation among integrable lattIce models, quiver gauge theories, and hidden TQFT structure. His first talk was a sort of lecture on TQFT and integrable lattice model at an elementary level. At the beginning of the first talk, he explained quantum mechanics (QM). Then as a variant of QM, he introduced an axiomatic definition of topological quantum field theory as a special class of quantum field theory. He also introduced lattice model which can be seen as a discrete version of quantum field theories. In particular, he mentioned the integrability of the 1-dimensional Ising model. In the second talk, he focused on the correspondence between Wilson-'t Hooft lines in a class of quantum gauge theories and transfer matrices in the corresponding integrable lattice models. At first, he gave an explanation of “classical integrability” and “quantum integrability” for field theories. In the case of 2-dimensional lattice model, he explained that the integrability is described by the Yang-Baxter equation. Then he moved on to the details of the correspondence. In the lattice model side of the correspondence, he described the transfer matrix in terms of n-copies of L-operators. Moreover, in order to compare to the gauge theory side, he took the trigonometric limit and rewrote the transfer matrix by “more fundamental” L-operators. The gauge theory side is in particular given by 4d N=2 n-node circular quiver theory. The theory is defined on a 4d twisted spacetime S^1 xε R^2 x R, and he gave an expression of the Wilson-'t Hooft line wrapping the circle S^1. As the main result of his joint work with Kazunobu Maruyoshi and Junya Yagi, he gave a relation between these Wilson-’t Hooft lines and transfer matrices. Finally, he gave several comments related to integrability from TQFT in extra dimension.

2020-10-02

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DMWG seminar by Dr. Ishiyama: a spectacular cosmological N-body simulation

Visible components of our Universe, such as galaxies, show hierarchical structures. Such structures are always embedded in DM structures called "halos". In the early Universe, there exist small density fluctuations that eventually collapse to halos at some points by their self-gravity. Then, halos grow to form larger structures again by self-gravity and this is the origin of the structure of the current Universe. The large-scale structure of halos as well as their inner structures contain information about the nature of the DM particle. Cosmological N-body simulation is a powerful computational method to follow that structure formation, by solving multi-body problems numerically. A halo, which is a clump of elementary DM particles, is treated as one smooth particle in N-body simulation. Its prediction power is so strong that the calculation corresponding to the upcoming cosmological survey, for example, has long been awaited. However, its computational costs scale as the square of the particle number N (or N log N when some reduction methods are adopted) and it is almost impossible to cover everything we need. There are two strategies in the calculation: simulating a large volume with large particle mass, or a small volume with small particle mass. The former is suitable for studies that deal with the large-scale structure while the latter has advantages in studying the properties of each halo. His group has conducted a large high-resolution simulation project which enables us to study both of them. The Uchuu simulation, which uses the cubic of 12800 particles in a 2 Gpc-scale simulation box, enables us to study large-scale structures. The Shin-Uchuu simulation in the same project, which uses the cubic of 6400 particles in a 140 Mpc-scale box, is provided aiming to study the inner structure of DM halos. Analyzing the simulated structure and halo properties, the matter power spectrum covering from the largest to the non-linear regime is obtained. Also, the so-called mass-concentration relation in a wide halo mass range is now available thanks to the project. There is another good news for DM hunters: the results of the simulation are open to the public. This should boost the DM study from many aspects!

2020-09-25

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Biology Seminar by Dr. Kyosuke Adachi on September 23, 2020

On September 23rd, Kyosuke Adachi gave a talk at the iTHEMS Biology Seminar on phase transitions in Biology. He first introduced the concept of phase transition and its possible application to understanding a number of biological phenomena. Then, he talked about his research on modelling the structural transition of chromatin states, and also about equilibrium and non-equilibrium dynamics. His research is really nice in how it engages both biologists and physicists, and many people seemed to enjoy his talk. In particular, the topic of chromatin dynamics is an area many molecular biologists are interested in at the moment, and we will be looking forward to hearing about his progress in the future.

2020-09-18

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Biology Seminar by Dr. Hye Jin Park on September 16, 2020

On 16th September, Hye Jin Park (Asia Pacific Center for Theoretical Physics; APCTP) gave us a talk about her work on eco-evolutionary dynamics. She specifically looked at what if there are novel mutations that generate a nonexistent phenotype (temporal emergence of different phenotypes) and how it affects the evolution of cyclic dominance. She took advantage of introducing novel phenotypes to construct phylogenetic-alike trees, which contain some information for which types are similar or dissimilar. She found that similar types are unlikely to exhibit cyclic dominance. We discussed how we can apply the theory to real systems and what factors are important. Thank you so much, Hye Jin for the fantastic talk! -Ryosuke Iritani

2020-09-11

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Math Seminar by Dr. Ken Furukawa on September 8, 2020

On September 8, there was a math seminar by Dr. Ken Furukawa. He gave a talk entitled Maximal Regularity and Partial Differential Equations. In the first part of his talk, the speaker explained the maximal regularity of parabolic partial differential equations and various sufficient conditions for the maximal regularity. Especially he introduced some functional calculus to obtain the analytic semigroup. In the second part, the speaker explained his recent collaboration work on the primitive equation and its relationship to the Navier-Stokes equation. He first shows that we can formally obtain primitive equations from the Navier-Stokes equation on the thin domain. He then explained his recent collaboration work which justifies this formal derivation of the primitive equation and how the sufficient conditions in the first talk work.

2020-09-09

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Biology Seminar by Dr. Masashi Tachikawa on September 9, 2020

On 9th September, Masashi Tachikawa (Kyoto University) gave us a talk on adaptive dynamics as a framework for evolutionary dynamics. He first gave us a quick overview for modeling evolution, and then introduced adaptive dynamics toolbox and pairwise invasibility plots to visualize trait-substitution processes towards evolutionarily singular points. He finally talked about how to capture evolutionary branching (two morphs emerging) using envelope with a trait value being tuned as-if a parameter. We all excitedly learned a lot from this talk. Thank you, Masashi! -Ryosuke Iritani

2020-09-04

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Biology Seminar by Dr. Miki Ebisuya on July 17, 2020

In 1638, Galileo Galilei proposed “the square-cube law”: the ratio of two volumes is greater than the ratio of their surfaces. This law enables us to understand why large animals like elephants need longer time to cool their body temperature than small ones like human. On July 17th, Miki Ebisuya at European Molecular Biology Laboratory (EMBL) explained why human needs longer time to develop her/his body than mouse, at the iTHEMS seminar. In fact, the speed of the segment formation ("taisetsu" in Japanese) of human is twice or three times as slow as that of mouse. By combining state-of-the-art experiments and a model with two variables, her group discovered that the difference of tempos is due to the difference of biochemical parameters. The talk was clear and enjoyable. And it was accessible to the diverse audience. As a mathematician asked during the talk, their discovery raises a new fundamental question about why reactions in human are slower than those in mouse. The question might be also answered by the collaboration between biology and mathematics in a future.

2020-09-03

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iTHEMS Math-Phys joint seminar was held on August 31 and September 1, 2020

The iTHEMS Math-Phys joint seminar was held on August 31st and September 1st, inviting Makiko Sasada from University of Tokyo and Kenichi Bannai from Keio university / RIKEN AIP. This was a series of lectures entitled “Geometric Perspective for the Theory of Hydrodynamic Limits”. They explained to us their recent joint work with Yukio Kametani on hydrodynamic limits from algebraic/geometric view point. On Day 1, Sasada-san gave an introduction to hydrodynamic limits, and explained the motivation of the joint work and the key ideas. One of the goals of the theory of hydrodynamic limits is to derive macroscopic dynamics from microscopic evolution equations rigorously. There have been many results to this problem, but all of them depend on specific microscopic models. The long term goal of this joint work is to construct an abstract and universal theory of hydrodynamic limits. One of the most important ingredients of the theory of hydrodynamic limits is the “decomposition of closed forms”, which have been obtained by Varadhan and other people using very technical argument depending on models. One of the aims of this work is to give a more general and clear understanding of this type of decompositions. Their strategy is as follows: the microscopic data can be divided into topological (geometric) part and stochastic (analytic) part. For discrete models, the former one is modeled by a directed graph, the set of states at each vertex, and the interaction through edges. A typical analytic datum is the jump rate, i.e., the frequency of interaction. They observed that some important feature of hydrodynamic limits depends only on the geometric data, and as a consequence, they could avoid ad-hoc analytic estimations. Moreover, they obtain a version of Varadhan’s decomposition in a very general setting. On Day 2, Bannai-san gave a precise mathematical formulation of their main results and proofs. As explained above, the geometric part of microscopic model is given by a directed graph, a pointed set of states, and a function which represents the interaction through edges. From this set of data, we can form a configuration space, each point of which corresponds to a possible state on the graph (The interaction data induce the transition structure on the configuration space). On the configuration space, they consider a special type of functions / forms called “uniformly local functions / forms”, and construct a cohomology theory (uniformly local cohomology) associated to them. Surprisingly, the uniformly local cohomology captures all conserved quantities (macroscopic observables). Moreover, from this fact, they can derive a local form version of Varadhan’s decomposition. An important ingredient of the proof is the group cohomology, which is often used in the field of number theory. They assume the existence of a free group action on the graph (which is valid in many important examples), and apply a general theory of group cohomology. It is very surprising that a fundamental result in hydrodynamic limits is derived from an abstract algebraic theory, and it will provide us a new and clear understanding of this field.

2020-09-03

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Biology Short Talk by Dr. Ryosuke Iritani on September 2, 2020

On September 2, Ryosuke Iritani gave a lecture at iTHMES Biology Seminar. In this seminar, Ryo explained the principles of evolution in an easy-to-understand way, using examples such as the diversification of pet dogs and cruciferous plants, and changes in the structure of the gecko's hands. Especially, the formulation of adaptive evolution using Fokker planck equarion was introduced. His seminar will be very useful as a basic knowledge of evolutionary biology and mathematical biology that will be covered in future seminars.

2020-08-27

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Biology Seminar by Dr. Gen Kurosawa on August 26, 2020

On August 26th, Gen Kurosawa gave a talk at the iTHEMS Biology seminar. The main topic of the talk was biological timing, and he introduced his work on mathematical modelling of circadian rhythm and hibernation. In addition, he also talked about his current effort in trying to apply theories developed in biology to understand the transaction network between companies. He clearly made a lot of effort to make the seminar accessible and enjoyable to people without background knowledge, and I'm sure many people appreciated that.

2020-08-22

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iTHEMS Theoretical Physics Seminar by Dr. Takuya Shimazaki on August 21, 2020

On August 21st (Fri.), Takuya Shimazaki (The University of Tokyo) gave an iTHEMS-phys seminar on an application of the Lefschetz thimble method to the Schwinger mechanism, or a particle production problem caused by strong electric fields. In the seminar, he has demonstrated a new formulation to estimate the particle production rate. The new formulation gives a good result even in some regimes where one cannot use the Dykhne–Davis–Pechukas (DDP) formula (a commonly used approximation in a two-level quantum system equivalent to the Schwinger mechanism). There were a lot of lively discussions, and the audience looked enjoying the seminar.

2020-08-05

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Biology Seminar by Dr. Lukasz Kusmierz on August 5, 2020

On 5th August, Ph.D. Lukasz Kusmierz ( RIKEN Center for Brain Science ) gave a talk at the iTHEMS Biology Seminar. Dr. Kusmierz introduced us to his work that modeling of heavy tails in the distribution of synaptic weights in the brain. His modeling, called "Cauchy network" which is based on the Cauchy distribution, has been successful in recreating biologically distributions. It could serve as a useful framework for checking the effects of synaptic heavy tails in various scenarios. His research will be a major step forward in the future of neuroscience. Thank you very much, Lukasz!

2020-08-05

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Math Seminar by Dr. Tadahiro Miyao

The iTHEMS Math seminar entitled "Stability of ferromagnetism in many-electron systems”, by Dr. Tadahiro Miyao, was held on 31 July. In the first part, the speaker reviewed basic properties of electron and introduced the Hubbard model, which describes interacting electrons. In addition, he constructed a model independent framework describing stabilities of ferromagnetism in strongly correlated electron systems. Especially, he reinterpreted the famous Marshall-Lieb-Mattis theorem and Lieb’s theorem. Then he showed that Lieb’s theorem still holds true even if the electron-phonon and electron-photon interactions are taken into account. As examples, he explained the Holstein-Hubbard model and the Kondo lattice model. Finally, he also mentioned other stability classes and open problems. In the second part, the speaker introduced order preserving operator inequalities and many mathematical tools, such as the Perron-Frobenius-Faris theorem, abstract reflection positivity, the hole-particle transformation, and so on. He also explained how these inequalities are applied to the mathematical study of ferromagnetism. Then Lieb's theorem of the Hubbard model and its stabilities were discussed in terms of the inequalities.

2020-07-31

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Biology Seminar by Dr. Takashi Okada on July 29, 2020

On 29th July, Takashi Okada gave us a talk on his work on population genetics theory. He first explained that the classical Wright-Fisher demography cannot inherently consider the realistic situation in which the offspring-number distribution is skewed. Second, he talked about what if we extend the Wright-Fisher demography to a skewed offspring number (power low distribution), showing us that the power-low distribution can dramatically change the timescale of evolution (e.g., sojourn time of fixation of a neutral mutant) as well as large population size limits. We learned that even the classic theory arising from Sewall Wright and Ronald A Fisher entails mathematical expansion. Thank you so much, Takashi, for the great talk!

2020-07-27

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Special DMWG seminar : The latest results from the XENON1T experiment

XENON1T collaboration has reported interesting results in June, which could be the signature of the physics beyond the standard model. We held a special DMWG seminar on July 22, inviting Prof. Yamashita, who is a specialist in the XENON1T data analysis, from Nagoya University. Many people from various research fields have registered and participated in this online seminar. The number of registrants is more than 180 while the participants than 100. We first would like to apologize to our guests, especially to whom could not attend the seminar although they have registered due to our trouble with the webinar system. XENON1T is an experiment aiming to detect the scattering between dark matter (DM) and a xenon nucleus. Xenon is one of the best targets material for WIMP (Weakly Interacting Massive Particle) because of its stability and the large atomic number. By setting the detector deep underground, the cosmic-ray scattering event, which is the main source of the background, is efficiently removed. The original experiment was started in 2005 (XENON10) and after several upgrades, XENON1T has completed its first observing run in 2018. The signature of the so-called nuclear recoil event is searched to detect WIMP. There is another type of event referred to as the electronic recoil event, which is also useful to detect other DM signatures, and this seminar focuses on such a kind of event. The target region of the DM parameter space is different between these two event types. The 285 electronic recoil events over the expected 217-247 from the background are observed in the recoil energy range of 1-7keV during the 1st observing run of the XENON1T experiment. In this talk, Prof. Yamashita has explained the details of the analysis and the possible interpretation of the signature. Starting from the introductions about the possible background considered in the traditional analysis, the statistical treatments, and also the model fitting results are provided. There are several possibilities for explaining the excess: (i) tritium background, (ii) solar axion, (iii) anomalous neutrino magnetic moment, and (iv) bosonic DM. If the excess is explained by tritium (i), it means that we have detected the first tritium background events while others indicate the detection of the signatures of the new physics. Solar axion (ii) could fit the recoil spectrum beautifully, however, there may not be consistent with the results from astrophysical observations. The neutrino scenario (iii) is another possibility with less significance, and the significance of the bosonic DM scenario (iv) could not over the 3.0 sigma. The excess itself is convincing while it is difficult to conclude its origin. Abobe-mentioned possibilities are planned to be tested with further upgrades of the XENON1T experiment, XENONnT. We should be excited about the results in the near future. Stay tuned!

2020-07-20

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Math seminar by Dr. Yuichi Ike on July 15, 2020

We have all heard that "data is the new oil". But just like any fossil resource, data also has to be worked with to use it effectively. In his talk, titled "Topological data analysis from a practical and mathematical perspective", Dr. Yuichi Ike from Fujitsu highlighted several mathematical aspects of data processing as well as relevant applications in the health sector. In the first part of the talk, the audience was introduced to basic concepts of topological data analysis. The goal of this technique is to infer the shape of data - i.e. topological quantities such as the number of connected components, loops, cavities, etc. - from the input data points. While the shape is represented by the homology group in the continuous case, the discrete case calls for different methodology. One possible technique is the creation of persistence diagrams to identify critical components. In a general application workflow, these approaches appear as follows. From the input data, its persistent homology is computed, visualized via a persistence diagram, and finally passed on to experts for evaluation. This has applications in material sciences and time series analysis as well as medical settings. Here, a recent work of the speaker was able to reduce misclassifications in a diagnosis setting by up to 70%. The second part of the talk was devoted to the mathematical foundations of the presented work, namely on persistence-like distance on the sheaf category and displacement energy. Starting from elements in symplectic geometry, via a Morse theory for sheaves, the speaker integrated several mathematical fields. Finally, after introducing the non-displacement theorem, the audience learned about several proofs in the field. Thus, the talk nicely tied current relevant applications to deep results in theoretical mathematics.

2020-07-16

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Biology Seminar about "Application of geometry to protein structure analysis" on July 15, 2020

In Biology Seminar on 15th July, a graduate student Haru Oono-Negami (Engineering department, University of Tokyo) talked about a general overview of the interdisciplinary topic between geometry and protein biology, as well as her own work on the protein-classification algorithms based on topological properties. Understanding and predicting the function of structurally "similar" proteins is of pivotal importance to any field of biology. Her work extends previous studies that classify the topological structure of proteins in a computationally reasonable time still with a good accuracy. We audience, after her talk, excitedly discussed extensions and background problems behind her talk. Thank you so much for the great talk, Haru-san! - Ryosuke Iritani

2020-07-16

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DMWG seminar on July 13 by Dr. Michimura

The Michelson interferometer is sensitive to the new physics as well as to the gravitational wave. The input laser beam is split in the horizontal and vertical direction, then combined again after times of the round trip in the cavity of each path. The patters of the interference give us the information about the change in path length, forces shifting the reflecting mirrors, and/or the change in the speed of light. During the observing run searching for the gravitational waves, a high-intensity laser form the input source is supplied continuously so it is highly efficient if we can make use of the laser to probe other physics simultaneously. Let us focus on the laser beams after the split. The polarization of the split laser beam changes at each time it is reflected. When axion (or axion-like particle, ALP) coupled to photon exists, the velocity of the right- and left-handed polarized waves should be different. Hence by setting the "bow-tie" cavity to realize different path-length for the right- and left-handed polarized photons, we should see the signature of the ALP in the interference pattern. This idea, which is proposed by Dr. Michimura and his colleagues, is completely new and enable us to probe the unexplored region for ALP lighter than ~0.1 micro-eV. Furthermore, this new search can be done during the gravitational-wave observations and do not affect such observations. He also has shown the expected sensitivity for scalar and vector DM picking up well-motivated examples and told us another idea for the experiment. Such new ideas should open new ways to access the nature of dark matter!

2020-07-08

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Biology Seminar by Dr. Yui Uchida on July 8, 2020

On 8th July, Ph.D. Yui Uchida (RIKEN BDR) gave a talk at the iTHEMS Biology Seminar. Dr. Uchida introduced to us the research field of Evolutionary Developmentary biology (EvoDevo) and talked about her researches on embryogenesis. Her lecture gave a briefly explanation about the background of EvdDevo in general and the important evolutionary questions in vertebrate development that had been tackled by her with mathematical modeling of embryogenesis. I felt her lecture helped many audiences to understand EvoDevo and we had a good discussion. Another highlight of her talk was her talk on the evolution of the five fingers of Tetrapoda excited the physicists! Thank you very much, Dr. Uchida.

2020-07-02

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Biology Seminar by Dr. Shingo Gibo on July 1, 2020

On 1 July, Shingo Gibo gave a talk at the iTHEMS Biology Seminar. He talked about his research on using mathematical approaches to understand biological oscillations, such as circadian rhythms. His work is a really nice example of the synergy between different disciplines. He draws ideas from mathematics and physics to solve problems in life science, and then his results developed in life science feeds back to various areas related to mathematics and physics. Another highlight of his talk was his cute zoom background :-) -Jeffrey Fawcett

2020-07-01

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Math seminar by Dr. Ryusuke Hamazaki on Jun 24, 2020

The iTHEMS Math seminar entitled "Universal Error Bound for Constrained Quantum Dynamics" by Dr. Ryusuke Hamazaki, was held on 24 Jun. In the first part, the speaker first introduced two physical examples of constrained dynamics including Rydberg atoms. Then, he explained the motivation of his study: finding quantitative error estimates of constrained-dynamics in generic gapped quantum systems. He introduced his result about a universal and rigorous error bound for a constrained-dynamics approximation in generic gapped quantum systems. Then, he gave the outline of the proof of the error bound. The proof uses the Schrieffer-Wolf transformation (SWT) and Sylvester equation. In the second talk, he gave a more precise proof of the error bound. In the proof, several computational techniques are used.

2020-06-25

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Dark Matter Working Group Seminar on June 22, 2020

Astrophysical observations are really important for understanding the nature of dark matter (DM) in multiple aspects. For example, the measurement of the temperature evolution of the neutron star (NS) provides us with new information about the properties of weakly interacting massive particle (WIMP). Since WIMP can interact with nucleon, of which scattering process is intensively searched in direct detection experiments, WIMP in our Universe should be captured by NSs. When the accumulated WIMPs annihilate inside the NS they heat up to modify the temperature evolution of the NS. Such a phenomenon is especially to probe the WIMP in the mass range of m<O(0.1)GeV and m>O(100)TeV, i.e., the range where it is difficult to probe with on-Earth experiments. In order to detect the effect of the WIMP annihilation, one must understand the temperature evolution of the NS in the standard model process accurately. In general, the surface temperature of NS is the highest at their birth, then cools through the photon and neutrino emission. Some of the NS older than ~Myr shows a higher temperature from the simple expectation in the standard model processes and the gap between the observation and the theoretical prediction was believed to be a room for the DM heating. In the above discussion, the processes of the direct and modified Urca, Bremsstrahlung, and Cooper-pair braking & formation are considered. But another important process so-called the rotochemical heating exists for rotating NSs. The beta equilibrium is not sustained when the NS is rotating and the conversion of the neutron to the proton occurs more frequently than its inverse process. NS heating through this process should be involved when we predict the temperature evolution. The deviation from the beta equilibrium hence the temperature evolution is sensitive to the birth period of the NS. Based on the calculation involiving a detailed treatment of the NS inner structure, Dr. Hamguchi has shown in this seminar that the rotochemical heating should be more efficient than that from the WIMP annihilation for a typical birth period. There might be no rooms for the WIMP annihilation to heat up the NS. However, the observational estimate of the birth period is still a challenging task, and there could be NSs with high birth periods. Furthermore, the number of such systems that are suitable for testing the WIMP heating scenario will increase in the near future. Such kinds of study should accelerate the collaboration between kinds of experiments to solve the DM mystery.

2020-06-23

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Math seminar by professor Tasuku Soma

In 17 June, professor Tasuku Soma (The university of Tokyo) gave a seminar on scaling problem and information geometry at the math seminar. In the first part he gave an introductory talk on scaling problem. Assume matrix A is given and each entry of A is positive. Matrix scaling problem is to find good matrix L,R with which LAR and (LAR)* has nice property. He then introduced Sinkhorn algorithm. This is an algorithm to calculate "LAR" in the above problem. He then explained operator scaling, which is quantum analogue of matrix scaling. He explained his recent result on the operator scaling and information geometry. It is known by Csizar that Sinkhorn algorithm for matrix scaling is actually an alternating e-projection, which appears in the information geometry. He then introduced his recent work with Takeru Matsuda. In that work, they proved that operator scaling is also an alternating e-projection.

2020-06-19

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Report on iTHEMS Intensive Course by Dr. Yoh Iwasa - Sex expression and sex allocation of marine organisms

This month, we hold 4-day intensive course of mathematical biology. This is especially for non-expert. On June 18th, Dr. Yoh Iwasa talked about various mysteries of sex. For instance, anemonefishes (kumanomi, in Japanese) are male when they are born. As they get bigger, they become female. Interestingly, some coral reef fishes are opposite. As they get bigger, they become male. Why do they show such sex expressions? Dr. Iwasa astonished us that various mysteries of sex can be resolved from the view point of game theory. According to him, “Anything related to sexual system can be quantified. In terms of the number of offspring, number of reproductive success, and other things. Success of the male depends on whether there are many more males or females. Obviously, this is the game theoretic view point.” During the lecture, the philosophy behind the mathematical modeling was explained in detail. The lecture on Thursday was attended by more than 160 people through Zoom and Youtube. Dr. Iwasa answered all the uncountable questions from the audience. The wonderful intensive course continues. - Gen Kurosawa

2020-06-15

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Biology Seminar by Dr. Martin Skrodzki on June 10, 2020

On 10th June, Martin Skrodzki talked about Turing models. Historically, Turing's models have been very successful to describe various pattern-formations on a two dimensional plane. He briefly introduced examples and then talked about three dimensional space, showing amazingly diverse patterns the model can cover. His talk generated stimulation discussion among the audience. Thank you so much for the great talk, Martin! -Ryosuke Iritani

2020-06-15

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”Field theoretical approach to relativistic hydrodynamics" on June 12, 2020.

The iTHEMS Theoretical Physics Seminar is hold on June 12, 2020. The speaker is Masaru Hongo in University of Illinois at Chicago/RIKEN iTHEMS. The title is ”Field theoretical approach to relativistic hydrodynamics”. Hydrodynamics is a low-energy effective theory of a conserved charge density, which describes a long-distance and long-time behavior of many-body systems. It is applicable not only to a non-relativistic weakly-interacting dilute gas but also a relativistic strongly-interacting dense liquid like a quark-gluon plasma. The main purpose of this seminar is to explain how we can derive the hydrodynamic equation from the underlying field-theoretical description of systems [1-3]. The derivation is based on the recent development of non-equilibrium statistical mechanics, and they show that the procedure to derive hydrodynamic equations is similar to the so-called renormalized/optimized perturbation theory. Also, to describe transport phenomena in local thermal equilibrium, they give a path-integral formula for a thermodynamic functional, which results in the emergence of thermally induced curved spacetime [2]. These results enable us to derive hydrodynamic equation based on quantum field theories.

2020-06-15

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Dark Matter Working Group Seminar on June 12, 2020

Among the numbers of dark matter (DM) scenarios, Weakly Interacting Massive Particle (WIMP) is one of the best-studied particles. It attracts special attention because of its beautiful mechanism to achieve the relic abundance of dark matter which is referred to as the thermal freeze-out. In the early Universe, the annihilation of the WIMP into the standard model (SM) particles and its inverse process are frequent enough to sustain the thermal equilibrium. At a certain point, WIMP decouples from the thermal bath then its number density, which is directly related to the relic abundance, is fixed. The strength of the coupling between WIMP and the SM sector determines the annihilation frequency. The same coupling is also responsible for the energy transfer between the SM particles and WIMP. The constraints on that scattering cross-section (i.e., the energy transfer between two sectors) have already been severely constrained by direct detection experiments. This motivates us to consider such a model that the coupling is so small and the relic abundance is achieved by a resonant annihilation at a certain mass. In this way, we can satisfy the requirements from the results of direct detection experiments. The small coupling between the SM sector and WIMP could lead to a non-equilibrium between them around the freeze-out epoch. Such a situation is referred to as the kinetic decoupling. The kinetic decoupling before the freeze-out affects the calculation of the relic density, which is a crucial part of the WIMP scenario. In this talk, Dr. Abe clarified the effect of the kinetic decoupling in terms of the coupling constant taking two examples of fermionic and scalar DM in the Higgs portal scenario. He calculated the freeze-out process in detail and showed that the scattering cross-section, which is measured at direct detection experiments, should also be different from the case where assumes a complete thermal equilibrium. We could see the signature of such DM in near-future experiments. We should carefully work on the synergy between different types of experiments in this high-precision era of DM search.

2020-06-05

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Biology Seminar by Dr. Hiroshi Yokota on June 3, 2020

In the 6th biology seminar, Hiroshi Yokota (iTHEMS fellow at Kyoto University) talked about his theoretical work on the energy of chromosome loop structure (collaborative work with Masashi Tachikawa). Through the modeling, he talked about the possibility that the chromosome loop structure may occur due to ATP hydrolysis. His work will stimulate future debate over the source of the energy needed for chromosome loops to occur. Great talk, Hiroshi! -Ryosuke Iritani

2020-06-01

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QFT-core Seminar by Dr. Ryusuke Hamazaki on May 29, 2020

The second QFT-core seminar entitled “Localization and universality in non-Hermitian many-body systems” given by Dr. Ryusuke Hamazaki (RIKEN Hakubi/iTHEMS) was held on May 29. Non-Hermitian physics is now one of the topics studied actively, and he is one of the world-leading physicists of this topic. In the seminar, first, he introduced the basic ideas of thermalization of the isolated quantum systems and non-Hermitian physics with simple examples. After that, some cutting-edge progress of non-Hermitian many-body localization, and universality of non-Hermitian random matrices were introduced. The seminar was held via the Zoom online conference system. Around 20 people participated in the seminar and joined the active discussion.

2020-06-01

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Biology Seminar on May 27, 2020

On 27 May, Ayaka Kato, The University of Tokyo, gave a talk at the 6th iTHEMS Biology Seminar. In this seminar, Ayaka talked about the results of the research on mathematical modeling of dopamine-related phenomena. It was not previously known how dopamine is involved in motivation, but in Ayaka's previous studies, the mathematical model from several previous experiments was proposed. In this seminar, Ayaka presented a new model that incorporates learning decay and successfully reproduces the real behavior on a computer simulation based on her new model. Since modeling the relationship between dopamine and motivation is very important both psychologically and medically, I felt that the results of these studies would not only benefit basic research but would also serve as a basis for general-purpose practical science and improve their research motivation.

2020-05-29

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Math Seminar by Dr. Masaki Taniguchi

The iTHEMS Math seminar entitled "Knotted 2-spheres in the 4-space and Yang-Mills gauge theory," by Dr. Masaki Taniguchi, was held on 27 May. In the first part, the speaker reviewed that classical knot theory and history of knot. Especially, he introduced that one and two dimensional knot theory, and gave many examples. For one dimensional knot theory, he explained the fundamental problem of knot theory, i.e., the problem of classifying 1-knots up to equivalent. As an example, he introduced a knot invariant coming from 3-colorings. For two dimensional knot theory, he explained the problem of how we write diagrams of 2-knots in four dimensional Euclidean space. Then he introduced the motion picture. In the second part, the speaker focuses on a problem considered in differential topology. First, he explained that the fundamental problem in differential topology. Next, he introduced gauge theory and some examples. Finally, as the main result of the talk, he explained his theorem about the difference between continuous and smooth two dimensional knots. He then introduced that the proof uses Yang-Mills gauge theory for 4-manifolds obtained by the surgery of 2-knots.

2020-05-25

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QFT-core Seminar “Gradient Flow Equation and Its Applications” on May 15, 2020

The QFT-core seminar series has been started from this fiscal year. The seminar series is hold under the theme of the Quantum Field Theory including elementary particle theory, nuclear theory and Condensed Matter physics. The First seminar in the series was given by Dr.Kengo Kikuchi from the Riken iTHEMS on May 15. The title is “Gradient Flow Equation and Its Applications”. The gradient flow is the one of the methods to suppress the ultraviolet divergence in gauge theories. The any correlation functions in terms of the flowed field, which is defined by the gradient flow equation, are finite without additional renormalizations. Because of this surprising property, the methods has been studied widely, especially in the lattice field theory. In this seminar, he introduce what the gradient flow is briefly, and show his work, “generalized gradient flow equation”, which is the gradient flow equation for field theories with nonlinearly realized symmetry. Applying the formalism to a supersymmetric theory and O(N) non linear sigma model, the SUSY gradient flow and the Large N gradient flow are obtained. He also refer to the current research, the gradient flow of the supersymmetric theory with the non-renormalization theorem and the new formalism to obtain the sphalerons, which is one of the static classical solutions, using gradient flow methods. The seminar was hold via Zoom. There were about 20 participants from iTHEMS and other university. The participants enjoyed meaningful discussions through the seminar.

2020-05-20

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First virtual Math Seminar on May 1, 2020

The first iTHEMS Math seminar of this academic year was held on May 1st on Zoom, inviting our colleague Keita Mikami. The title of the talk was “From Eigenvalues to Resonances”. The main topic was Resonance, which is one of the most studied objects in mathematical study of Schrödinger operators. In the first part, the speaker briefly reviewed spectral theory and how we use it in the study of Schrödinger operators, introducing some basic notions used in the study of Schrödinger operators. Especially, he explained that spectra can be classified into eigenvalues and continuous spectra. Then he introduced scattering theory, which can be used to analyze absolutely continuous spectra. One novelty is that generalized eigenfunction has a representation formula in terms of scattering matrices. In the second part, the speaker gave a brief introduction of resonances and its application to both mathematicians and researchers in other fields. After introducing mathematical definition of resonances, he explained its applications in the other fields. One example was the following experimental result; when one makes a wave with certain frequency in aquarium, there appears special pattern in the distribution of speed. This phenomena can be explained mathematically by considering resonance of pseudodifferential operator on torus.

2020-05-15

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Math Seminar by Dr. Yukimi Goto

Math seminar titled "How many electrons can atoms bind?" by Dr. Yukimi Goto was hold on 13 May. In the first part, the speaker started the talk by introducing many body Hamiltonian and Pauli principle. She then introduced the ionization conjecture. She also introduced some known results concerning about this conjecture. In the second part, the speaker introduced approximation methods and its relation to the ionization conjecture. She first introduced Thomas-Fermi theory and see TF functional appears as a leading term of grand state energy for large atom. She introduced Hartree-Fock theory next. She mentioned a variant of the ionization conjecture for HF theory was proven by Solovej, but original conjecture is still open. She then explained HF theory can be regarded as good approximation in terms of volume.

2020-05-13

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Biology Seminar by Dr. Catherine Beauchemin on May 13, 2020

Catherine talked about her general approach for formalizing and quantifying the principle of virological dynamics, namely “virophysics.” She first presented compartmental models to generalize the probability distribution of sojourn time of cells being infective, with parameter estimation in flu data using MCMC, and then talked about COVID-19 modeling and its predictability. I was honestly surprised that increasing the number of compartments can readily change the distribution, and found it promising to apply her approach to not only virology but ecology and evolution as well. Thank you, Catherine, for the great talk! - Ryosuke Iritani