Shin Ichi Tanabe

Plasmon transport in graphene investigated by time-resolved electrical measurements

Plasmons, which are collective charge oscillations, could provide a means of confining electromagnetic field to nanoscale structures. Recently, plasmonics using graphene have attracted interest, particularly because of the tunable plasmon dispersion, which will be useful for tunable frequency in cavity applications. However, the carrier density dependence of the dispersion is weak (proportional to n1/4) and it is difficult to tune the frequency over orders of magnitude. Here, by exploiting electronic excitation and detection, we carry out time-resolved measurements of a charge pulse travelling in a plasmon mode in graphene corresponding to the gigahertz range. We demonstrate that the plasmon velocity can be changed over two orders of magnitude by applying a magnetic field B and by screening the plasmon electric field with a gate metal; at high B, edge magnetoplasmons, which are plasmons localized at the sample edge, are formed and their velocity depends on B, n and the gate screening effect.

Evaluation of thermal comfort using combined multi-node thermoregulation (65MN) and radiation models and computational fluid dynamics (CFD)

The 65-node thermoregulation model was developed, based on the Stolwijk model. The model has 16 body segments corresponding to the thermal manikin, each consisting of four layers for core, muscle, fat and skin. The 65th node in the model is the central blood compartment, which exchanges convective heat with all other nodes via the blood flow. Convective and radiant heat transfer coefficients and clothing insulation were derived from the thermal manikin experiments. A thermoregulation model combined with radiation exchange model and computational fluid dynamics (CFD) is proposed. The comprehensive simulation method is described.

Comfort limits for asymmetric thermal radiation

Abstract Groups of 32 and 16 subjects of both sexes were exposed in an environmental chamber to radiant asymmetry caused by a cool wall, a warm wall, and a cool ceiling. Each subject was tested individually while seated and clothed at 0.6 clo. During each 3.5-hour experiment the subject was exposed to six radiant temperature asymmetries. He was asked whether and where he experienced any local cool or warm sensation, and whether it was felt to be uncomfortable. During the entire experiment he was kept thermally neutral by changing the air temperature according to his wishes. For cool walls, warm walls, and cool ceilings curves have been established showing the percentage of dissatisfied subjects as a function of the radiant asymmetry. Radiant asymmetry at a warm wall caused less discomfort than a cool wall. A cool ceiling caused less discomfort than a warm ceiling. Accepting that 5% of the subjects may feel uncomfortable. a radiant temperature asymmetry of 10°C is allowable at a cool wall, 23°C at a warm wall, and 14°C under a cool ceiling. A previous study showed that 4°C is allowable under a warm ceiling. Radiant asymmetry had no significant impact on the operative temperatures preferred by the subjects. No significant differences were observed between the responses of men and women exposed to radiant asymmetry.

Differences in perception of indoor environment between Japanese and non-Japanese workers

Field surveys were conducted at an office with multinational workers in Japan to investigate the differences in the way groups of occupants perceive the environment under real working conditions. Returned questionnaires, 406 in total, were classified into three groups according to their nationality and sex. Only 26% of workers reported their working environment to be comfortable. A significant neutral temperature difference of 3.1 °C was observed between the Japanese female group and the non-Japanese male group under their usual working conditions. Japanese females reported a higher frequency of sick building syndrome related symptoms compared to other groups. Occupant comfort and reported frequency of SBS symptoms were closely related to deviation of the thermal sensation vote from neutral. The thermal environment was found to be a major factor affecting occupant comfort in the concerned office. Differences in the perception of the indoor environment were negatively affecting the ratings of their working environment.

EFFECT OF HUMIDITY AND SMALL AIR MOVEMENT ON THERMAL COMFORT UNDER A RADIANT COOLING CEILING BY SUBJECTIVE EXPERIMENTS

Abstract Radiant air-conditioning systems are expected to be more comfortable and superior energy-saving systems than convective air conditioning ones generally used. There are some studies on radiant cooling systems. However, they were seldom put to practical use because of dew point problem in Japan. The objective of this study is to investigate the thermal comfort of local parts of the body and the whole body, in particular, including the effects of humidity (45% rh, 65% rh, 85% rh) and small air movements, by subjective experiments under a radiant cooling system. The experiments have been performed by using radiant cooling panels in a climate chamber. Subjects were seated on a chair under the radiant cooling panels, and voted their thermal sensation and comfortable sensation. The following results were obtained. Even in the radiant cooling system, the influence of humidity and small air movement on thermal sensation votes of the whole body could be correctly estimated by using a standard new effective temperature (SET*) within one scale error of thermal sensation. Small air movement with the radiant cooling system had a possibility of improving the comfortable sensation votes in the radiant cooling.

Testing and optimizing the performance of a floor-based task conditioning system

Abstract During recent years an increasing amount of attention has been paid to air distribution systems that individually condition the immediate environments of office workers within their workstations. As with task lighting systems, the controls for these ‘task conditioning’ systems are partially or entirely decentralized and under the control of the occupants. Among the primary types of task conditioning systems (floor-, desktop- and partition-based), floor-based designs are the most common, having been widely developed and used in South Africa and Europe, and are now gaining acceptance in the United States. This paper reports the results of recently completed laboratory measurements investigating the thermal performance of a floor-based task conditioning system. The experiments were performed in a controlled environment chamber configured to resemble a modern office space with modular workstation furniture and partitions. Tests were conducted to study the effects of supply volume, supply temperature, supply direction, and heat load levels in the space. In addition to detailed temperature and velocity measurements, a new skin-temperature-controlled thermal manikin was used to evaluate the non-uniform thermal environments produced by the floor-based system, in both sitting and standing positions. Under the low to intermediate supply volumes investigated in this study, the overall performance of the floor-based system resembled that of displacement ventilation systems. Primarily by controlling supply volume the floor-based system can be operated to maintain acceptable thermal comfort in the occupied zone of the building, while at the same time taking advantage of the temperature stratification inherent in displacement flow to achieve savings in space conditioning energy use.

Half-Integer Quantum Hall Effect in Gate-Controlled Epitaxial Graphene Devices

High-quality monolayer graphene was grown on the Si face of SiC by thermal decomposition, and its electrical properties were investigated in top-gated devices. At 2 K, the carrier mobility of the graphene exceeded 10,000 cm2 V-1 s-1 and the half-integer quantum Hall effect was observed. The quantum Hall states were even observed at various carrier densities when top-gate bias was applied. These findings suggest high-quality epitaxial graphene possesses the unique nature of monolayer graphene and is robust against device fabrication, which holds potential for graphene-based electronics applications.

Formation of organic indoor air pollutants by UV-curing chemistry

UV-curable systems for manufacturing of furniture and parquet form a major and growing field in radiation curing. Numerous types and combinations of photoinitiators have been developed for crosslinking of acrylated systems and unsaturated polyesters. The properties of the photoinitiators being used in these materials must fulfill requirements like low toxicity, low odor and high reactivity. However, volatile reaction products being produced during the photochemical process contribute to the pollution of indoor air by emission from the surface and may cause strong odor and adverse health effects. Therefore, the release of photoinitiators, fragmentation products and monomers from UV-cured coatings was studied as a function of time under realistic living conditions in emission test chambers and cells. Main components detected in the chamber air were benzaldehyde, cyclohexanone, benzophenone and acrylate monomers. The area-specific emission rates SERA were found to be strongly dependent on the climatic conditions.

Growth and electronic transport properties of epitaxial graphene on SiC

With the aim of developing a single-crystal graphene substrate indispensable to graphenes practical applications, we are investigating the structural and physical properties of graphene epitaxially grown on SiC by thermal decomposition. We grow monolayer and bilayer graphene uniformly on a micrometre scale on the Si face of SiC in an Ar environment and in ultra-high vacuum, respectively. Epitaxial bilayer graphene, even if uniform in thickness, contains two types of domains with different stacking orders. We compare the transport properties of monolayer and bilayer graphene using top-gate Hall bar devices. Quantum Hall effects are observed in monolayer graphene and a band gap is electrically detected in bilayer graphene. The monolayer and bilayer graphene show quite different transport properties, reflecting their electronic structures.

Effective radiation area of human body calculated by a numerical simulation

A numerical simulation method is developed for predicting the effective radiation area and the projected area of a human body for any posture. This method is based on the solar heat gain simulation for buildings. To confirm the validity of the present method, predicted effective radiation area factors and projected area factors for both standing and seated persons are compared with those by the measurements. It was found that predicted values agree quite well with those by the subjective experiments within 10% accuracy. The effective radiation area and the diagrams of the projected area factors for a person sitting on the floor are illustrated. Moreover, the angle factors between a standing person and rectangular planes are calculated and compared with the results by Fanger.