arXiv subjects

Ryo Takahashi

Publications and source records attributed to Ryo Takahashi.

At least 37 records · Page 2Linked to original sources

arXiv2025

Ultra-low-power ring-based wireless tinymouse

Wireless mouse rings offer subtle, reliable pointing interactions for wearable computing platforms. However, the small battery below 27 mAh in the miniature rings restricts the ring's continuous lifespan to just 1-10 hours, because current low-powered wireless communication such as BLE is power-consuming for ring's continuous use. The ring's short lifespan frequently disrupts users' mouse use with the need for frequent charging. This paper presents picoRing mouse, enabling a continuous ring-based mouse interaction with ultra-low-powered ring-to-wristband wireless communication. picoRing mouse employs a coil-based impedance sensing named semi-passive inductive telemetry, allowing a wristband coil to capture a unique frequency response of a nearby ring coil via a sensitive inductive coupling between the coils. The ring coil converts the corresponding user's mouse input into the unique frequency response via an up to 449 uW mouse-driven modulation system. Therefore, the continuous use of picoRing mouse can last approximately 600 (8hrs use/day)-1000 (4hrs use/day) hours on a single charge of a 27 mAh battery while supporting subtle thumb-to-index scrolling and pressing interactions in real-world wearable computing situations.

cs.HC↗

arXiv2025

Full-body WPT: wireless powering with meandered e-textiles

We present Full-body WPT, wireless power networking around the human body using a meandered textile coil. Unlike traditional inductive systems that emit strong fields into the deep tissue inside the body, the meander coil enables localized generation of strong magnetic field constrained to the skin surface, even when scaled to the size of the human body. Such localized inductive system enhances both safety and efficiency of wireless power around the body. Furthermore, the use of low-loss conductive yarn achieve energy-efficient and lightweight design. We analyze the performance of our design through simulations and experimental prototypes, demonstrating high power transfer efficiency and adaptability to user movement and posture. Our system provides a safe and efficient distributed power network using meandered textile coils integrated into wearable materials, highlighting the potential of body-centric wireless power networking as a foundational layer for ubiquitous health monitoring, augmented reality, and human-machine interaction systems.

cs.HC↗

arXiv2025

A Bidirectional Power Router for Traceable Multi-energy Management

To address challenges in improving self-consumption of renewables and resilience in local residential power systems, the earlier work of the authors introduced a novel multi-energy management concept, integrating bidirectional power routing and electricity-hydrogen conversion. This paper focuses on an experimental verification of the bidirectional power router based on line-switching, the essential hardware to realize the concept. The primary contribution is the validation of the router's capability to handle dynamic change of bidirectional power flow. Furthermore, to achieve bidirectional power routing without affecting the smooth and stable operation of the power system, a novel algorithm for router's switching is designed based on power flow monitoring. The effectiveness of the proposed method is demonstrated through an experiment using a setup with a commercially available stationary battery.

eess.SY↗

arXiv2025

Extension-closed subcategories over hypersurfaces of finite or countable CM-representation type

Let k be an algebraically closed uncountable field of characteristic zero. Let R be a complete local hypersurface over k. Denote by CM(R) the category of maximal Cohen-Macaulay R-modules and by D^{sg}(R) the singularity category of R. Denote by CM_0(R) the full category of CM(R) consisting of modules that are locally free on the punctured spectrum of R, and by D^{sg}_0(R) the full subcategory of D^{sg}(R) consisting of objects that are locally zero on the punctured spectrum of R. In this paper, under the assumption that R has finite or countable CM-representation type, we completely classify the extension-closed subcategories of CM_0(R) in dimension at most two, and the extension-closed subcategories of D^{sg}_0(R) in arbitrary dimension.

math.AC↗

arXiv2025

Wireless charging and readout via textile coil for continuous full-body wearable computing

The growing use of wearable devices for activity tracking, healthcare, and haptics faces challenges due to the bulkiness and short lifespan of batteries. Integration of a textile-based wireless charging and readout system into everyday clothing can enable seamless power supply and data collection around the body. However, expanding such system to cover the entire body is challenging, as it increases electromagnetic interference with the body, degrading the performance of wireless system. This article introduces a meandered textile coil designed for body-scale, efficient wireless charging and readout. The meander coil can confine a strong inductive field near the body surface, ensuring W-class safe charging and sensitive readout with uW-class low power. Moreover, its zigzag design is simple enough for mass production on industrial knitting machines. Therefore, the body-scale meander coil can continuously operate battery-free wearable devices across the body, leading to ubiquitous deployment of continuous full-body wearable computing into everyday clothing.

cs.HC↗

arXiv2025

Full-body NFC: body-scale near-field sensor networks with machine-knittable meandered e-textiles

Wireless body networks comprising battery-free on-body sensors and textile-based wireless readers can enable daily health monitoring and activity tracking by continuously monitoring physiological signals across the body. However, previous textile-based wireless networks made of coils or antennas have limited the data and power transmission area because covering the whole body results in undesirable levels of electromagnetic interactions with the body, degrading the scalability, power consumption, and data rate. Here, we report Full-body NFC, digitally-knitted electronic textiles based on a twin meander coil design that enables body-scale near-field communication (NFC) with battery-free sensor tags arbitrarily placed around the body. Full-body NFC features i) a meander coil that enhances the magnetic field intensity on the body's surface while suppressing undesired interactions with deep tissues, in addition to ii) paired identical coil structure that enables highly-sensitive and motion-robust NFC using a differential architecture. Additionally, industrial digital knitting machines loaded with conductive yarn allow the integration of the Full-body NFC system into daily garments supporting approximately $70-80\%$ large-scale NFC-enabled area of the body. We demonstrate Full-body NFC could achieve mW-class energy-efficient near-field sensor networks with hundreds of kbps-class NFC battery-free sensor tags occupying less than $0.3\%$ of the coverage area under severe body movements.

cs.HC↗

arXiv2025

Vector space summands of lower syzygies

In this paper, we investigate problems concerning when the residue field $k$ of a local ring $(R,\frak m$, $k)$ appears as a direct summand of syzygy modules, from two perspectives. First, we prove that the following conditions are equivalent: (i) $k$ is a direct summand of second syzygies of all non-free finitely generated $R$-modules; (ii) $k$ is a direct summand of third syzygies of all non-free finitely generated $R$-modules; (iii) $k$ is a direct summand of $\frak m$. We also prove various consequences of these conditions. The second point of this article is to investigate for what artinian local rings $R$ the dual $E^*=Hom_R(E_R(k),R)$ of the injective envelope of the residue field, which is also a second syzygy, is a $k$-vector space. Using the notion of Eliahou-Kervaire resolution, we introduce a large class of artinian local rings that satisfy this condition.

math.AC↗

arXiv2025

Joint-repositionable Inner-wireless Planar Snake Robot

Bio-inspired multi-joint snake robots offer the advantages of terrain adaptability due to their limbless structure and high flexibility. However, a series of dozens of motor units in typical multiple-joint snake robots results in a heavy body structure and hundreds of watts of high power consumption. This paper presents a joint-repositionable, inner-wireless snake robot that enables multi-joint-like locomotion using a low-powered underactuated mechanism. The snake robot, consisting of a series of flexible passive links, can dynamically change its joint coupling configuration by repositioning motor-driven joint units along rack gears inside the robot. Additionally, a soft robot skin wirelessly powers the internal joint units, avoiding the risk of wire tangling and disconnection caused by the movable joint units. The combination of the joint-repositionable mechanism and the wireless-charging-enabled soft skin achieves a high degree of bending, along with a lightweight structure of 1.3 kg and energy-efficient wireless power transmission of 7.6 watts.

cs.RO↗

arXiv2025

Demo of picoRing mouse: an ultra-low-powered wireless mouse ring with ring-to-wristband coil-based impedance sensing

Wireless mouse rings offer subtle, reliable pointing interactions for wearable computing platforms, but the small battery below 27 mAh in the miniature rings restricts the ring's continuous lifespan to just 1-2 hours due to the power consumption of current low-powered wireless communication like BLE. However, the picoRing mouse addresses this by enabling continuous ring-based mouse interaction with ultra-low-powered ring-to-wristband wireless communication through a coil-based impedance sensing method called semi-passive inductive telemetry. This allows a wristband coil to capture a unique frequency response of a nearby ring coil via sensitive inductive coupling, converting the user's mouse input into the unique frequency response via an 820 uW mouse-driven modulation module. Thus, the continuous use of picoRing mouse can potentially last over 92 hours on a single charge of a 20 mAh battery while supporting subtle scrolling and pressing interactions.

cs.HC↗

arXiv2025

Failure of the Lefschetz property for the Graphic Matroid

We consider the strong Lefschetz property for standard graded Artinian Gorenstein algebras. Such an algebra has a presentation of the quotient algebra of the ring of the differential polynomials modulo the annihilator of some homogeneous polynomial. There is a characterization of the strong Lefschetz property for such an algebra by the non-degeneracy of the higher Hessian matrix of the homogeneous polynomial. Maeno and Numata conjectured that if such an algebra is defined by the basis generating polynomial of any matroid, then it has the strong Lefschetz property. For this conjecture, we give counterexamples that are associated with graphic matroids. We prove the degeneracy of the higher Hessian matrix by constructing a non-zero element in the kernel of that matrix.

math.AC↗

arXiv2024

Plug-n-play e-knit: prototyping large-area e-textiles using machine-knitted magnetically-repositionable sensor networks

Prototyping electronic textile (e-textile) involves embedding electronic components into fabrics to develop smart clothing with specific functionalities. However, this process is still challenging since the complicated wiring setup is required during experimental phases. This paper presents plug-n-play e-knit, a large-scale, repositionable e-textile for providing trial-and-error prototyping platforms across the textile. Plug-n-play e-knit leverages industrial digital knitting machines loaded with conductive thread to automatically embed a communication and power supply network into garments, in addition to using soft magnet connectors to rearrange electronic components while preserving the stretchability of the garment. These combinations enable users to quickly establish e-textile sensor networks, and moreover test the performance and optimal placement of the electric devices on the textile. We demonstrated that our textiles leveraging custom I2C protocols could achieve the motion-resilient motion-tracking sensor network over a 2700 $cm^2$ garment area.

cs.HC↗

arXiv2024

Friction jointing of distributed rigid capacitors to stretchable liquid metal coil for full-body wireless charging clothing

For full-body wireless power transfer (WPT), a liquid metal (LM)-based meandered textile coil has been proposed. Multiple rigid capacitors must be inserted in a long coil for efficiency; however, the conventional adhesive jointing suffers from the fragile connection between a rubber tube filled with LM and the capacitor due to the poor adhesion of the rubbers. This paper presents a friction-based jointing, which covers the capacitor with a rigid capsule to enhance the frictional force between the tube and capsule. By experimentally optimizing the capsule design, the LM coil with capacitors showed 3.1 times higher stretch tolerance (31.8 N) and 3.5 times higher bending tolerance (25.9 N) than the adhesive jointing. Moreover, the WPT garment prototype shows excellent mechanical durability against repeated stretching and washing over 100 times. Our full-body meandered textile coil can enable wireless charging to wearable devices around the body for long-term continuous healthcare monitoring, activity recognition, and AR/VR.

cs.HC↗

arXiv2024

picoRing: battery-free rings for subtle thumb-to-index input

Smart rings for subtle, reliable finger input offer an attractive path for ubiquitous interaction with wearable computing platforms. However, compared to ordinary rings worn for cultural or fashion reasons, smart rings are much bulkier and less comfortable, largely due to the space required for a battery, which also limits the space available for sensors. This paper presents picoRing, a flexible sensing architecture that enables a variety of \textit{battery-free} smart rings paired with a wristband. By inductively connecting a wristband-based sensitive reader coil with a ring-based fully-passive sensor coil, picoRing enables the wristband to stably detect the passive response from the ring via a weak inductive coupling. We demonstrate four different rings that support thumb-to-finger interactions like pressing, sliding, or scrolling. When users perform these interactions, the corresponding ring converts each input into a unique passive response through a network of passive switches. Combining the coil-based sensitive readout with the fully-passive ring design enables a tiny ring that weighs as little as 1.5 g and achieves a 13 cm stable readout despite finger bending, and proximity to metal.

cs.HC↗

arXiv2024

A System of Bidirectional Power Routing Toward Multi-energy Management

In this paper, we propose a system of bidirectional power routing for inter-house multi-energy management systems that utilize electricity and hydrogen as energy carriers. The key is to share private facilities such as photovoltaic panels and batteries among a group of houses along with a common hydrogen system. A power router of line switching type is introduced as a physical interface to realize the sharing economy between households. The proposed system offers a unique measure to address the urgent challenges of today's multi-energy system, namely increasing the renewables' self-consumption, enhancing the energy system's resilience, and providing traceability of hydrogen in terms of renewability certification. We also present an experimental demonstration under a simplified scenario using prototype hardware.

eess.SY↗

arXiv2024

On the vanishing of self extensions of even-periodic modules

In this paper we study rigid modules over commutative Noetherian local rings, establish new freeness criteria for certain periodic rigid modules, and extend several results from the literature. Along the way, we prove general Ext vanishing results over Cohen-Macaulay rings and investigate modules which have zero class in the reduced Grothendieck group with rational coefficients.

math.AC↗

arXiv2024

Bulk-entanglement spectrum correspondence in $PT$- and $PC$-symmetric topological insulators and superconductors

In this study, we discuss a new type of bulk-boundary correspondence which holds for topological insulators and superconductors when the parity-time ($PT$) and/or parity-particle-hole ($PC$) symmetry are present. In these systems, even when the bulk topology is nontrivial, the edge spectrum is generally gapped, and thus the conventional bulk-boundary correspondence does not hold. We find that, instead of the edge spectrum, the single-particle entanglement spectrum becomes gapless when the bulk topology is nontrivial: i.e., the $\textit{bulk-entanglement}$ $\textit{spectrum}$ $\textit{correspondence}$ holds in $PT$- and/or $PC$-symmetric topological insulators and superconductors. After showing the correspondence using $K$-theoretic approach, we provide concrete models for each symmetry class up to three dimensions where nontrivial topology due to $PT$ and/or $PC$ is expected. An implication of our results is that, when the bulk topology under $PT$ and/or $PC$ symmetry is nontrivial, the non-interacting many-body entanglement spectrum is multiply degenerate in one dimension and is gapless in two or higher dimensions.

cond-mat.mes-hall↗

arXiv2024

Expansions of the Potts model partition function along deletions and contractions

We establish two expansions of the Potts model partition function of a graph. One is along the deletions of a graph, a rewritten formula given in Biggs (1977). The other is along the contractions of a graph. Then, we specialize the partition function to the chromatic or flow polynomial by the Möbius inversion formula, and prove two known equations of the two polynomials. One expresses the chromatic polynomial as a weighted sum of flow polynomials of deletions, the other expresses the flow polynomial as a weighted sum of chromatic polynomials of contractions. The proof of the former by Biggs formula is due to Bychkov et al. (2021). The two expressions are considered to be dual in the sense of their forms, and transfer to each other with plane duality. This relation also holds in our expansions of the Potts model partition function. We clarify this duality by using matroid duality. Partition functions can be extended to matroids, and the two expansions can also be extended. The two expansions transfer to each other with matroid duality, so in addition to an elementary combinatorial proof of the two, we give another proof by the "duality" relation between them.

math.CO↗

arXiv2024

Non-Hermitian skin effect enforced by nonsymmorphic symmetries

Crystal symmetries play an essential role in band structures of non-Hermitian Hamiltonian. In this paper, we propose a non-Hermitian skin effect (NHSE) enforced by nonsymmorphic symmetries. We show that the NHSE inevitably occurs if a two-dimensional non-Hermitian system satisfies conditions derived from the nonsymmorphic symmetry of the doubled Hermitian Hamiltonian. This NHSE occurs in symmetry classes with and without time-reversal symmetry. The NHSE enforced by nonsymmorphic symmetries always occurs simultaneously with the closing of the point gap at zero energy. We also show that such a NHSE can occur in specific three-dimensional space groups with nonsymmorphic symmetries.

cond-mat.mes-hall↗