Takayuki Hiraoka
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takayukihir.bsky.social
Takayuki Hiraoka
@takayukihir.bsky.social
130 followers 180 following 74 posts
Studying complex systems and network science. Postdoc at Aalto University.

I oppose any violence against civilians and devastation of their lives.

🌐 https://sites.google.com/view/takayukihiraoka/
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takayukihir.bsky.social
A semi-regular reminder: My colleagues and I are running an interdisciplinary online seminar series called Complex Systems Research Exchange (CREx🦖).
sites.google.com/view/cxrex
Home page of the Complex Systems Research Exchange website. It reads: Complex Systems Research Exchange (CREx) is an online seminar series aimed at building an international research community in the interdisciplinary field of complex systems, very broadly defined. Our focus is on creating opportunities to hear from early to mid-career researchers about their research, while also serving as a platform for networking and collaboration. We are open to a wide range of research areas including network science, nonlinear dynamics, dynamical systems, computational social science, science of science, machine learning and AI, data science, urban science and human mobility, mathematical biology and ecology, neuroscience, and more. Please subscribe to the mailing list to receive announcements of upcoming seminars. The Zoom link for each seminar will be sent to the mailing list shortly before the seminar. Please reach out to organizers if you are interested in giving a presentation yourself or know someone who would be interested. This seminar series is run on a volunteer basis and is currently organized without funding. Organizers: Jeehye Choi, Takayuki Hiraoka, Inho Hong, Hyewon Kim, Kazuki Nakajima, Ayumi Ozawa, Taekho You
November 3, 2025 at 10:13 AM
takayukihir.bsky.social
A world map showing the locations of cities that hosted/will host international scientific conferences in 2025 and 2026. NetSci 2025 Maastricht, IC2S2 2025 Norkköping, and CCS 2025 Siena are on the left-hand side, while NetSci 2026 Boston, IC2S2 2026 Burlington, and CCS 2026 Binghamton are close together on the right-hand side.
September 6, 2025 at 3:13 PM
takayukihir.bsky.social
To sum up, we found that: (1) while degree heterogeneity promotes the effect of high-degree bias, thereby reinforcing disease-induced herd immunity, (2) spatiality enhances the effect of immunity localization, which weakens disease-induced herd immunity.
Schematic figure showing the two drivers of disease-induced herd immunity, each influenced by an associated structural feature of the contact network. High-degree bias of immunity is enhanced by degree heterogeneity and has a positive effect on disease-induced herd immunity. Topological localization of immunity is enhanced by spatiality and has a negative effect on disease-induced herd immunity.
July 19, 2025 at 4:50 PM
takayukihir.bsky.social
I guess this schematic figure says it all—In a network model, infection can only propagate from a node to a neighbor. Thus, immunity is necessarily localized in a contiguous part of the network. This is in contrast to random immunization, in which immunity is distributed evenly in the population.
An illustrative figure comparing disease-induced immunity (left) and randomly distributed immunity (right) in the same network. Disease-induced immunity is clustered in one corner of the network, while random immunity is evenly distributed in the network, creating many interface edges with susceptible nodes.
July 19, 2025 at 4:50 PM
takayukihir.bsky.social
We found that toponyms show spatial specificity in their occurrence, unlike many common nouns. Interestingly, toponyms and common nouns describing places (e.g., “park”) behave differently from other common nouns (e.g., “music”) and toponyms referring to places outside the observation area.
A bar chart showing the dissimilarity of empirical data from the location-independent model for different words.
June 29, 2025 at 2:03 PM
takayukihir.bsky.social
However, quantitative studies of toponyms have been scarce.

In our new article in PLOS One, Takashi Kirimura, Naoya Fujiwara and I tried to address this gap by using a dataset of 400 million geotagged Twitter posts to study the association between toponyms and geography.
Geographic distribution of the occurrence of the word "Fukuoka", plotted on a map of Japan.
June 29, 2025 at 2:03 PM
takayukihir.bsky.social
On Tuesday, Tarmo Nurmi successfully defended his thesis on multilayer networks. Congratulations, Tarmo!
Tarmo Nurmi presents his thesis in front of the opponent, custos, and audience in a lecture room. From left to right: the custos Prof. Mikko Kivelä, the doctoral student Tarmo Nurmi, and the opponent Prof. Nataša Pržulj, after the defence.
June 19, 2025 at 3:48 PM
takayukihir.bsky.social
My bus is delayed, time for another beer
A glass of beer on a table in an outdoor café
June 6, 2025 at 1:51 PM
takayukihir.bsky.social
I just learned about loop-else syntax in Python and it made my day! docs.python.org/3/tutorial/c...
Screenshot from the Python documentation page linked in the text. It shows an example script of using an `else` clause paired with a `for` loop to search for prime numbers. The text below the script says: “(Yes, this is the correct code. Look closely: the `else` clause belongs to the `for` loop, **not** the `if` statement.)”
April 11, 2025 at 10:59 AM
takayukihir.bsky.social
Me ranting at AI about English words
Me: How come "ingenious" and "ingenuous" are two different words! They are so similar in spelling, yet they mean different things ChatGPT responds: Great observation! *Ingenious* and *ingenuous* do look incredibly similar, but their meanings are quite different because they come from different Latin roots. - **Ingenious** (meaning clever, inventive, or resourceful) comes from the Latin *ingeniosus*, which means "full of intellect or talent." This is related to *ingenium*, meaning "natural ability" or "cleverness." - **Ingenuous** (meaning innocent, straightforward, or naïve) comes from the Latin *ingenuus*, which originally meant "freeborn" or "noble," later evolving to mean "frank" or "open-hearted." Even though they look almost identical in modern English, their origins explain why their meanings are so different. It's one of those fun quirks of language! Me: And are you saying that "indigenous" is not related to either of them, with yet another origin? That's so confusing! ChatGPT responds: Yep, *indigenous* is from yet another root, even though it looks like it should be related! - **Indigenous** (meaning native or originating naturally in a place) comes from the Latin *indigenus*, which is based on *indu-* (meaning "within" or "in") and *gignere* (meaning "to beget" or "to produce"). So it literally means "born within" or "native to a place." So, despite their surface similarity: - **Ingenious** = clever, inventive (from *ingenium*, meaning "talent") - **Ingenuous** = innocent, open (from *ingenuus*, meaning "frank, freeborn") - **Indigenous** = native, originating in a place (from *indigenus*, meaning "born within") English is wild sometimes!
February 13, 2025 at 5:50 PM
takayukihir.bsky.social
A semi-regular reminder: Together with colleagues from South Korea and Japan, we are running an interdisciplinary online seminar series called Complex Systems Research Exchange (CREx🦖).
sites.google.com/view/cxrex
Home page of the Complex Systems Research Exchange website. It reads: Complex Systems Research Exchange (CREx) is an online seminar series aimed at building an international research community in the interdisciplinary field of complex systems, very broadly defined. Our focus is on creating opportunities to hear from early to mid-career researchers about their research, while also serving as a platform for networking and collaboration. We are open to a wide range of research areas including network science, nonlinear dynamics, dynamical systems, computational social science, science of science, machine learning and AI, data science, urban science and human mobility, mathematical biology and ecology, neuroscience, and more. Please subscribe to the mailing list to receive announcements of upcoming seminars. The Zoom link for each seminar will be sent to the mailing list shortly before the seminar. Please reach out to organizers if you are interested in giving a presentation yourself or know someone who would be interested. This seminar series is run on a volunteer basis and is currently organized without funding. Organizers: Jeehye Choi, Takayuki Hiraoka, Inho Hong, Hyewon Kim, Kazuki Nakajima, Ayumi Ozawa, Taekho You
January 15, 2025 at 12:00 PM
takayukihir.bsky.social
It’s always a pleasure to listen to Javier Ureña Carrion's lucid presentations, and his defence was no exception. Congratulations, Javier!
Javier giving his presentation at the defence in front of the audience. The opponent Prof. Esteban Moro, who joins the defence online, makes his observation. The doctoral student Javier Ureña Carrion (right) and the custos Prof. Mikko Kivelä (left), after the defence.
October 22, 2024 at 7:19 PM
takayukihir.bsky.social
Last Friday, Sara Heydari successfully defended her thesis! Congratulations! Unfortunately I couldn’t attend the defence in person, but I watched it over Zoom and it was brilliant.
Screenshot from the livestream of Sara’s defence. Sara in the middle is discussing her thesis with the opponent Jukka-Pekka Onnela in front of an audience.
September 12, 2024 at 6:38 AM
takayukihir.bsky.social
Ana Triana’s defence was a great success! Congratulations, Ana!
Ana starts her doctoral defence presentation. From left to right: the custos Prof. Jari Saramäki, the doctoral student Ana Triana and the opponent Prof. Joaquín Goñi, right after the defence.
August 23, 2024 at 2:59 PM
takayukihir.bsky.social
Last night in Helsinki.
A picture of auroras in the dark sky, glowing in purple and green.
August 13, 2024 at 2:39 PM
takayukihir.bsky.social
Together with my friends in South Korea and Japan, we are running an interdisciplinary online seminar series called Complex Systems Research Exchange (CREx🦖).
sites.google.com/view/cxrex/
Screenshot of the home page of the Complex Systems Research Exchange website
May 20, 2024 at 9:02 AM
takayukihir.bsky.social
Congratulations on the successful defence, Abbas! @abbasrizi.bsky.social
Abbas doing a cool hand gesture during his PhD defence, trying to convince the opponent and the audience From left to right: the custos Prof. Mikko Kivelä, the docoral student Abbas K. Rizi, and the opponent Prof. Nicola Perra, right after the defence
March 15, 2024 at 10:24 PM