Abstract Physically based rendering systems often support spectral rendering to simulate light transport in the real world. Material representations in such simulations need to be defined as spectral distributions. Since commonly available material data are in tristimulus colours, we ideally would like to obtain spectral distributions from tristimulus colours as an input to spectral rendering systems. Reproduction of spectral distributions given tristimulus colours, however, has been considered an ill‐posed problem since single tristimulus colour corresponds to a set of different spectra due to metamerism. We show how to resolve this problem using a data‐driven approach based on measured spectra and propose a practical algorithm that can faithfully reproduce a corresponding spectrum only from the given tristimulus colour. The key observation in colour science is that a natural measured spectrum is usually well approximated by a weighted sum of a few basis functions. We show how to reformulate conversion of tristimulus colours to spectra via principal component analysis. To improve accuracy of conversion, we propose a greedy clustering algorithm which minimizes reconstruction error. Using pre‐computation, the runtime computation is just a single matrix multiplication with an input tristimulus colour. Numerical experiments show that our method well reproduces the reference measured spectra using only the tristimulus colours as input.

Simulating the behavior of soap films and foams is a challenging task. A direct numerical simulation of films and foams via the Navier-Stokes equations is still computationally too expensive. We propose an alternative formulation inspired by geometric flow. Our model exploits the fact, according to Plateau's laws, that the steady state of a film is a union of constant mean curvature surfaces and minimal surfaces. Such surfaces are also well known as the steady state solutions of certain curvature flows. We show a link between the Navier-Stokes equations and a recent variant of mean curvature flow, called hyperbolic mean curvature flow , under the assumption of constant air pressure per enclosed region. Instead of using hyperbolic mean curvature flow as is, we propose to replace curvature by the gradient of the surface area functional. This formulation enables us to robustly handle non-manifold configurations; such junctions connecting multiple films are intractable with the traditional formulation using curvature. We also add explicit volume preservation to hyperbolic mean curvature flow, which in fact corresponds to the pressure term of the Navier-Stokes equations. Our method is simple, fast, robust, and consistent with Plateau's laws, which are all due to our reformulation of film dynamics as a geometric flow.

Genetic Algorithm is one of the most effective optimization algorithms, on which a lot of studies have been reported. Some studies on the application of island model, which is one of the representative methods to keep a diversity of solutions, to Multi-Objective Genetic Algorithm (MOGA) have been conducted. In MOGA, it is difficult to find the solutions which satisfy all objective functions because of their tradeoff. Especially when there are many objective functions, it is obvious that it needs a lot of time to search for effective Pareto solutions and find them. This paper proposes the interactive way of addition and deletion of islands to the original ones based on user's requirements with the visualization of acquired solutions in island model for MOGA. This paper applies the proposed method to Nurse Scheduling Problem (NSP) using the visualization by Principal Component Analysis (PCA). Through the experiment, it is confirmed that an interactive tuning of the weights for the objective functions leaded to the acquisition of better Pareto solutions which a user wants while they are difficult to be acquired by the prepared weights.

An RTD (resonant tunneling diode)-based flip-flop circuit with a new configuration is proposed. The circuit features an SCFL interface for both input and output, and achieves high-speed operation with a simplified configuration. The circuit consists of only two RTDs and three HEMTs, and works as a delayed flip-flop (D-FF) with return-to-zero (RZ) mode output. 50 Gbit/s operation is confirmed by SPICE simulation for the SCFL-interfaced D-FF with the proposed configuration. A static binary frequency divider (T-FF) is also designed based on the same concept. It is fabricated by InP-based RTD/HEMT integration technology, and its proper operation of up to 15 GHz is confirmed experimentally.

Ultrahigh-speed circuit applications of resonant tunneling diodes (RTDs) have been developed. One of the key concepts is the merged utilization of RTDs and high electron mobility transistors (HEMTs). The integration technology for InP-based RTDs and HEMTs has been developed. Another key technology developed is a circuit configuration using series-connected RTDs, driven by a clocked bias, in combination with HEMTs. Given this circuit concept, various kinds of edge-triggered flip-flop circuits and multiple-valued quantizers featuring high-speed operation and compact configuration have been constructed. By extending this circuit concept, an optoelectronic circuit using RTDs and a photodiode has also been developed. High-speed operations have been demonstrated, including a delayed-flip-flop circuit operating at 35 Gbit/s, multiple-valued quantizers operating at 10 GHz, a 2-bit analog-to-digital converter operating at 5 GHz and an optoelectronic circuit that demultiplexes an 80 Gbit/s optical signal into a 40 Gbit/s electrical signal. The presented results clearly show the potentiality of RTD-based circuits for the construction of unprecedented ultrahigh-speed communications and signal processing circuits.

A novel sampling phase detector (SPD) using a resonant-tunneling high electron mobility transistor (RTHEMT), which features strong nonlinear characteristics, is proposed and demonstrated as a means of achieving a simple, low-power-consumption SPD. We confirmed promising performance for an RTHEMT as a simple pulse generator in an SPD with low power consumption, even for a low reference-signal input level. An 11-GHz phase-locked oscillator is constructed along with the present SPD, and successfully phase-locked signals are obtained with it. These results clearly show the potential of constructing high-performance analog RF circuits based on RTHEMTs.