Impurity‐Induced First‐Order Phase Transitions in Highly Crystalline V2O3 Nanocrystals

A first‐order phase transition in a bulk material is generally considered to arise at extended defects such as grain boundaries or dislocations, where the energetic barrier between the two phases is reduced. Downsizing a crystal to the nanoscale can exclude the number of defects, leading to enhanced kinetic stabilization of the metastable phase. Here, the disappearance of the first‐order metal–insulator transition in defect‐free V₂O₃ nanocrystals and the revival of the transition by introducing a certain Cr or Ti impurity content are investigated. The hysteresis width of the transition corresponding to the barrier height decreases with the impurity content. It is proposed that homogeneous impurity doping is a universal method that can control the occurrence of a first‐order phase transition in nanoscale materials.     

Motion control of industrial robots by considering serial two-link robot arm model with joint nonlinearities

This paper presents a model based motion control approach for industrial robots by considering a serial two-link robot arm model with joint nonlinearities. In order to achieve the desired performance using the model based control approaches, it is important to obtain relevant models of both kinematics and dynamics including nonlinear characteristics. Main nonlinear components that lead to trajectory tracking errors of typical multi-axis industrial robot are joint nonlinearities in each axis and dynamic coupling effects between different axes. In this paper, a parametric modeling approach is introduced to reproduce behaviors of a serial two-link robot arm with joint nonlinearities. Nonlinear stiffness, angular transmission errors, and friction in these two links are directly identified as joint nonlinearities. This approach is applied for the serial two-link arm of a typical multi-axis industrial robot, which has low frequency vibration modes and significantly affects to the trajectory performance. Effectiveness of the modeling is verified by comparative studies with numerical simulations and experiments. Finally, a 2-DOF control scheme with the identified two-link dynamic model and a feedback loop-shaping with a variable notch filter are applied to improve the performance of trajectory tracking and residual vibration suppression.     

Stability tests of standard leaks for the calibration by a comparison method

At the calibration of standard leaks by a comparison method with reference standard leaks, important factors to evaluate the flow rates are the degrees of stability of a mass spectrometer leak detector (MSLD) and standard leaks. Stability of two leak element type standard leaks, a glass and a plastic, are tested. The test indicates that the warming up time is mainly influenced by the temperature of the mass spectrometer and 2 h is required to obtain a stabilized reading for the tested MSLD. In case of the glass type leak, 1 h pumping is required to obtain the stabilized flow rate after the exposure to the ambient air. In case of the plastic type leak, 1 min pumping is enough for the exposure time below 1 h but 6 h pumping is required after the 7 days exposure. After the valve closed duration within 3 h, the flow rates from both type of leaks recovered within a minute to 100% ± 0.5% of the averaged reading before the valve closed.     

Newly developed standard conductance element for in situ calibration of high vacuum gauges

A new leak element, which is named as “standard conductance element (SCE)”, has been developed for in situ calibration of ionization gauges (IGs) and quadrupole mass spectrometers (QMSs). The SCE is made of a stainless-steel sintered filter with the pore size of less than 1 μm. Since the gas flow through the SCE satisfies the molecular flow condition even at the pressure up to 10⁴ Pa, some useful characteristics of molecular flow are available. The SCE is supplied to users with a calibration certificate described its molecular conductance. Users can introduce optional test gases with the known flow rate to their vacuum chamber through the SCE in their laboratories. The overview of the SCE, the calibration method and recommended practices are introduced.     

Forging property,processing map,and mesoscale microstructural evolution modeling of a Ti-17 alloy with a lamellar (α+β) starting microstructure

Abstract

This work identifies microstructural conversion mechanisms during hot deformation (at temperatures ranging from 750 °C to 1050 °C and strain rates ranging from 10^?3 s^?1 to 1 s^?1) of a Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy with a lamellar starting microstructure and establishes constitutive formulae for predicting the microstructural evolution using finite-element analysis. In the α phase, lamellae kinking is the dominant mode in the higher strain rate region and dynamic globularization frequently occurs at higher temperatures. In the β phase, continuous dynamic recrystallization is the dominant mode below the transition temperature, T_β (880~890 °C). Dynamic recovery tends to be more active at conditions of lower strain rates and higher temperatures. At temperatures above T_β, continuous dynamic recrystallization of the β phase frequently occurs, especially in the lower strain rate region. A set of constitutive equations modeling the microstructural evolution and processing map characteristic are established by optimizing the experimental data and were later implemented in the DEFORM-3D software package. There is a satisfactory agreement between the experimental and simulated results, indicating that the established series of constitutive models can be used to reliably predict the properties of a Ti-17 alloy after forging in the (α+β) region.     

Optimal Total Planning for Incinerator Plants in an Urban Area

This paper proposes optimal total planning for incinerator plants (IPs) in a typical urban area, which includes a method of determining the number of plants and the capacities of the IPs. Burnable municipal refuse is disposed of sanitarily by high‐temperature incineration at the IPs. At the same time, power generation from waste (PGW) is being performed at many IPs to recover energy. At present, the amount of energy generated by PGW is greater than that of wind power or photovoltaic power generation. However, PGW has a limited generation efficiency and low generation output due to the smaller capacity of IPs. To overcome the above weakness, highly efficient PGW is necessary with total integration and scaling up of IPs. Regarding total integration and scaling up, operation in larger areas is favorable from the point of view of refuse volume and collection. In the planning stage, both the cost of IPs and refuse collection, which is important for refuse disposal, should be taken into account comprehensively. Optimal total planing for IPs can be performed in two stages. First, the disposal capacity G_k of an IP versus the number of plants K is decided by constraints. G_k is about the same for all K because of maintenance and refuse collection, and is greater than 300 tons per day in steps of 100 tons per day. G_k should be decided not only by refuse volume but also by cessation of operation at plants due to maintenance or faults. Second, the cost of each value of K is calculated based on the construction and operating costs of the IPs, income from selling the energy of PGW, and refuse collection costs. Therefore, the value of K with the minimum cost is selected as the optimal number of IPs. A numerical simulation of an area with a population of 3 million indicates that the optimal plant number is 4. At present there are eight or nine IPs in cities of 3 million people. The above cost reduction effect will be about 15% from the present value. Considering the situation of aging IPs, a decreasing trend in refuse volume, and the stringent financial conditions of local governments, the proposed method is very effective and realistic.     

Biodesulfurization of alkylated forms of dibenzothiophene and benzothiophene by Sphingomonas subarctica T7b

Sphingomonas subarctica T7b was isolated from soil in Toyotomi, Hokkaido, Japan as an organism capable of desulfurizing aromatic hydrocarbons in light gas oil (LGO) through enrichment culture. S. subarctica T7b could grow on mineral salt sulfur-free (MSSF) medium with the n-tetradecane oil phase containing dibenzothiophene (DBT), alkyl dibenzothiophenes (alkyl DBTs) or alkyl benzothiophenes (alkyl BTs) as the sole sulfur source and desulfurize these compounds, but could not utilize the tetradecane as a carbon source. This is the first report of a gram-negative bacterium which can desulfurize 4,6-dibutyl DBT and 4,6-dipentyl DBT. The desulfurized product of DBT produced by this strain was 2-hydroxybiphenyl, as in the case of other DBT-desulfurizing bacteria. S. subarctica T7b could desulfurize LGO and the sulfur content was decreased to 41% within 36 h.