Multi-wavelength intermittent photoluminescence of single CdSe quantum dots

A single chromophore detection using video-microscopy is one of the latest methodologies to reveal unique characteristics, which could not be obtained from ensemble measurements. Among many kinds of subjects, dynamic optical properties observed in colloidal semiconductor nanoparticles are attractive and important not only for the basis of photo-physics but also for application studies, e.g. biological labeling, electronic devices. In this study, fluorescence video-microscopy was performed on cadmium selenide (CdSe) quantum dots (QDs) spin-coated on a glass substrate. From single CdSe QDs detection, emissions at wavelengths separated over 60 nm were observed for the first time. This spectral feature was attributed to the existence of double-emissive relaxation processes in CdSe QDs. Photoluminescence intermittency was also observed both from relaxation processes. Fluorescence video-microscopy, which was advanced in biology, can be applicable for the real-time monitoring of dynamic properties in semiconductor photo-physics.     

Synthesis of Various Water-Soluble C60 Derivatives and Their Superoxide-Quenching Activity

Abstract

In order to examine the utility of fullerene as a medicinal application, we evaluated the reaction between fullerene derivatives and active oxygen species in vitro. This paper describes the synthesis of various water-soluble C₆₀ derivatives (cationic and anionic) and evaluation of their superoxide (O₂ ^?) quenching activity. Cationic C₆₀ derivatives showed fairly high efficiency.     

Synthesis of Various Water-Soluble G60 Derivatives and Their Superoxide-Quenching Activity

Abstract

In order to examine the utility of fullerene as a medicinal application, we evaluated the reaction between fullerene derivatives and active oxygen species in vitro. This paper describes the synthesis of various water-soluble C₆₀ derivatives (cationic and anionic) and evaluation of their superoxide (O₂ ^?) quenching activity. Cationic C₆₀ derivatives showed fairly high efficiency.     

Security measure allocation for industrial control systems: Exploiting systematic search techniques and submodularity

To protect industrial control systems from cyberattacks, multiple layers of security measures need to be allocated to prevent critical security vulnerabilities. However, both finding the critical vulnerabilities and then allocating security measures in a cost‐efficient way become challenging when the number of vulnerabilities and measures is large. This paper proposes a framework that can be used once this is the case. In our framework, the attacker exploits security vulnerabilities to gain control over some of the sensors and actuators. The critical vulnerabilities are those that are not complex to exploit and can lead to a large impact on the physical world through the compromised sensors and actuators. To find these vulnerabilities efficiently, we propose an algorithm that uses the nondecreasing properties of the impact and complexity functions and properties of the security measure allocation problem to speed up the search. Once the critical vulnerabilities are located, the security measure allocation problem reduces to an integer linear program. Since integer linear programs are NP‐hard in general, we reformulate this problem as a problem of minimizing a linear set function subject to a submodular constraint. A polynomial time greedy algorithm can then be applied to obtain a solution with guaranteed approximation bound. The applicability of our framework is demonstrated on a control system used for regulation of temperature within a building.     

Plutonium breeding of light water cooled fast reactors

Light water cooled fast reactor with new fuel assemblies (FA) has been studied for high breeding of fissile plutonium. It achieves fissile plutonium surviving ratio (FPSR) of 1.342 (discharge/loading), 1.013 end and beginning of equilibrium cycle (EOEC/BOEC), and compound system doubling time (CSDT) of 95.9 years at the average coolant density of pressurized water reactor (PWR). It is further improved for reduced moderation boiling water reactor (BWR) (RMWR) coolant density. Fissile plutonium surviving ratio reaches 1.397 (discharge/loading), 1.030 (EOEC/BOEC) and CSDT is 37 years. The present study has shown the possibility of breeding at the PWR coolant density and meeting the growth rate of energy demand of advanced countries at the RMWR and Super FR coolant density for the first time. The new FA consist of closely packed fuel rods. The integrity of welding of fuel rods at the top and bottom ends is maintained as the conventional fuel rods. The coolant to fuel volume fraction is reduced to 0.085, one-sixth of that of RMWR. The volume fraction remains unchanged with the diameter of the fuel rod. The thermal hydraulic design of the cores remains for the future study.     

Quantitative common cause failure modeling for auxiliary feedwater system involving the seismic-induced degradation of flood barriers

Flood barriers are important defenses which will reduce the internal flood-induced failure risk of safety-related equipment in the turbine building. Contrarily, the degradation of flood barriers will increase the risk of internal flood-induced common cause failure (CCF). Two layouts of auxiliary feedwater pumps system are compared to demonstrate the quantitative risk assessment of the possible degradation of flood barriers. The alpha decomposition method has been developed by the authors in order to quantitatively evaluate the CCF parameters based on the causal inference. Occurrence frequency and CCF triggering ability are two important elements which will decide the CCF risk significance of potential common causes. The seismic-induced internal flood combining with the degradation of flood barriers is analyzed. The degradation of flood barriers is treated as a stochastic process and a Markov model is applied to consider the time-dependent states. The failure time of three auxiliary feedwater pumps is calculated based on the water flow rate through flood barriers. CCF triggering abilities of internal floods are calculated which are represented as decomposed alpha factors. This article shows the updating process of CCF parameters according to Bayesian inference and hypothetical databases. It is concluded that the issue of CCF modeling is not only decided by the number of redundant components but also decided by causes and plant-specific design.     

Currents and Electric Fields Induced in Anatomically Realistic Human Models by Extremely Low Frequency Electric Fields

There is increasing public concern about biological interactions with and the potential health effects of low frequency electric and magnetic fields. Recently, the ICNIRP （International Commission on Non-Ionizing Radiation Protection） has published new exposure guidelines with regard to these fields. The aim of this paper is to demonstrate the calculation of the currents and electric fields induced in the human body by external electric fields at 60 Hz, using numerical human models of anatomically-realistic human bodies, and to compare those results with the basic restrictions proposed by the new guidelines. As a result, in the case that a human is exposed to an electric field of 1 kV/m at 60 Hz the short-circuit current of 18 μA flows though the ankles. Furthermore, the electric field of 40 mV/m in the nervous tissue of the adult model is induced by exposure to external electric fields at the reference level, which is enough smaller than the basic restrictions established in the ICNIRP guidelines for occupational exposure.     

Investigation of tribo-chemistry by means of stable isotopic tracers: Mechanism for durability of monomolecular boundary film

A monomolecular film of octadecanoic acid on a Si(1 0 0) surface was prepared using a computer-controlled Langmuir trough. The tribological properties were acquired by a ball-on-flat type tribo-tester under reciprocating motion. Considerable effects of ball material on lifetime for low friction were observed; a glass ball was excellent while a steel ball was poor. The rubbed surfaces on ball and flat were studied by time-of-flight secondary ion mass spectroscopy. Transfer of the carboxylic acid and silicon onto the ball surface from the flat specimen was found. The role of the transferred acid that prolongs the lifetime of low friction was proposed. It should be emphasized that deuterium-labeled carboxylic acid makes the target of TOF-SIMS analysis clear.