Efficient and precise cutting of zirconia ceramics using heated cutting tool

The thermally assisted machining of yttria-stabilized tetragonal zirconia polycrystal using a cutting tool heated with induction heating was proposed. Although the conventional thermally assisted machining cannot be applied to drilling, the proposed method can be. Heat transfer from the heated cutting tool to the workpiece was simulated analytically, and the result showed that heating of the tool up to 500 °C produced an increase of 150–400 °C in the workpiece temperature. Cutting experiments demonstrated an improvement in machinability.     

Hydrogenation and structural properties of Gd2Ni7 with superlattice structure

The crystal structure and hydrogenation properties of Ce₂Ni₇-type Gd₂Ni₇ were investigated by X-ray diffraction (XRD) and the hydrogen pressure–composition (P–C) isotherm. Ce₂Ni₇-type Gd₂Ni₇ was obtained by annealing at 1523 K for 12 h and quenching in ice water. Two superlattice reflections (002 and 004) of the Ce₂Ni₇-type were clearly observed at 2θ = 7.3° and 14.6° in the XRD profile. The refined lattice parameters were a = 0.49662(9) nm and c = 2.4255(3) nm, respectively. Two plateaus were clearly observed during the absorption–desorption process in the P–C isotherm. The first and second plateaus were at 0.015 and 0.13 MPa, respectively, in the first desorption. The maximum hydrogen capacity reached was 1.13 H/M. The enthalpy and entropy were calculated as −20 kJ/mol H₂ and −80 J/mol H₂ K, respectively, from the van’t Hoff plot. After the P–C isotherm, the GdNi₅ cell expanded by 2.15%, but the Gd₂Ni₄ cell shrank by 2.83%.     

A Water‐Soluble Mechanochromic Luminescent Pyrene Derivative Exhibiting Recovery of the Initial Photoluminescence Color in a High‐Humidity Environment

Switching of the luminescence properties of molecular materials in response to mechanical stimulation is of fundamental interest and also has a range of potential applications. Herein, a water‐soluble mechanochromic luminescent pyrene derivative having two hydrophilic dendrons is reported. This pyrene derivative is the first example of a mechanochromic luminescent organic compound that responds to relative humidity. Mechanical stimulation (grinding) of this pyrene derivative in the solid state results in a change of the photoluminescence from yellow to green. Subsequent exposure to water vapor induces recovery of the initial yellow photoluminescence. The color change is reversible through at least ten cycles. It is also demonstrated that this compound can be applied as a mechano‐sensing material in frictional wear testing for grease, owing to its immiscibility in non‐polar solvents and its non‐crystalline behavior. Transmission electron microscope and atomic force microscope observations of samples prepared from dilute aqueous solutions of the pyrene derivative on suitable substrates, together with dynamic light scattering measurements for the compound in aqueous solution, indicate that this amphiphilic dumbbell‐shaped molecule forms micelles in water.     

Properties of Hopfield model with the zero-order synaptic decay

In this paper, we investigate the effect of synaptogenesis on memories in the brain, using the abstract-associative memory model, Hopfield model with the zero-order synaptic decay. Using the numerical simulation, we demonstrate the possibility that synaptogenesis plays a role in maintaining recent memories embedded in the network while avoiding overloading. For the network consisting of 1000 units, it turned out that the minimum decay rate to avoid overloading is 0.02, and the optimal decay rate to maximize the storage capacity is 0.08. We also show that the average numbers of replacement synapses at each learning step corresponding to these two values are 1187 and 21024, respectively.     

To react or not to react? Intrinsic stochasticity of human control in virtual stick balancing

Understanding how humans control unstable systems is central to many research problems, with applications ranging from quiet standing to aircraft landing. Increasingly, much evidence appears in favour of event-driven control hypothesis: human operators only start actively controlling the system when the discrepancy between the current and desired system states becomes large enough. The event-driven models based on the concept of threshold can explain many features of the experimentally observed dynamics. However, much still remains unclear about the dynamics of human-controlled systems, which likely indicates that humans use more intricate control mechanisms. This paper argues that control activation in humans may be not threshold-driven, but instead intrinsically stochastic, noise-driven. Specifically, we suggest that control activation stems from stochastic interplay between the operator''s need to keep the controlled system near the goal state, on the one hand, and the tendency to postpone interrupting the system dynamics, on the other hand. We propose a model capturing this interplay and show that it matches the experimental data on human balancing of virtual overdamped stick. Our results illuminate that the noise-driven activation mechanism plays a crucial role at least in the considered task, and, hypothetically, in a broad range of human-controlled processes.     

Robust and accurate prediction of thermal error of machining centers under operations with cutting fluid supply

A novel temperature measuring system named LATSIS was proposed to realize a robust and accurate prediction of the thermal deformation of machining centers, even under external disturbances such as cutting fluid supply. LATSIS enables a drastic increase in the number of sensors employed for measuring the temperature of the machine tool. Thus, the entire temperature distribution can be obtained by interpolating the measured temperature 3-dimensionally without calculating the heat conduction. A set of experiments was conducted in which the LATSIS was employed to predict the TCP error. A total of 284 sensors were placed on the machining center, and the TCP error was predicted based on the measured temperature for the situation with/without the cutting fluid supply. The results of the prediction showed good agreement with the measured TCP error even during the initial transient temperature change as well as in the cooling phase after the machine halt. The TCP error with the cutting fluid supply is accurately predicted. LATSIS was proven to be a robust and accurate method for predicting the thermal deformation of machine tools, and is a promising technology for future manufacturing systems.     

Trap Levels in Eu and other Rare‐Earth Ions Codoped CaAl2O4 Phosphors

Photoluminescence spectrum, trap depths, and densities of trapped carriers of CaAl₂O₄:Eu phosphor crystals doped with rare‐earth elements were studied using the thermally stimulated luminescence technique. Trap depths and densities of the specimens vary with rare‐earth elements doped as the auxiliary activators. Tm and Nd are found to be effective for the strong afterglow phosphorescence peaking at λ = 442 nm for several hours after the excitation. CaAl₂O₄:Eu phosphor crystals doped with Nd and Tm include high density of carriers trapped at E = 0.59 and 0.52 eV, respectively.     

Development of a new heterojunction structure (ACJ -HIT) and its application to polycrystalline silicon solar cells

A new solar cell structure named HIT (Heterojunction with Intrinsic Thin layer) has been developed based on new artificially constructed junction (ACJ) technology. In this structure a non-doped a-Si thin layer was inserted between the p(a-Si)/n(c-Si) heterojunction, improving the output characteristics and achieving a conversion efficiency of 18.1%. This structure was applied to cast polycrystalline silicon solar cells of a practical size. A high conversion efficeincy of 13.6% was obtained with a cell size of 10 cm × 10 cm using various technologies, including hydrogen plasma passivation.