We measured high-speed sound propagation in a near-critical fluid using a ultra-sensitive interferometer to investigate adiabatic changes of fluids on acoustic timescales. A sound emitted by very weak continuous heating caused a stepwise adiabatic change at its front with a density change of order 10 −7 g/cm 3 and a temperature change of order 10 −5 deg. Very small heat inputs at a heater produced short acoustic pulses with width of order 10µsec, which were broadened as they moved through the cell and encountered with the boundaries. The pulse broadening became enhanced near the critical point. We also examined theoretically how sounds are emitted from a heater and how applied heat is transformed into mechanical work. Our predictions well agree with our data. Thermal equilibration in one-component fluids takes place increasingly faster near the gas-liquid critical point at fixed volume [1,2,3,4,5,6,7,8,9,10], despite the fact that the thermal diffusion constant D tends to zero at the criticality. This is because the thermal diffusion layer at the boundary expands and sounds emitted cause adiabatic compression and heating in the whole cell after many traversals in the container. This heating mechanism is much intensified near the critical point due to the critical enhancement of thermal expansion of the layer. If the boundary temperature T w is fixed, the interior temperature approaches T w on the timescale of the piston time [2],where L is the cell length and γ = C p /C V is the specificheat ratio growing near the critical point. This time is much shorter than the isobaric equilibration time L 2 /4D by the very small factor (γ − 1) −2 [11]. The previous experiments have detected only slow temperature and density changes in the interior region on timescales of order 1 sec. The aim of this letter is to report ultra-sensitive, high-speed observation of sound propagation through a cell filled with CO 2 on the critical isochore close to the critical point T c = 304.12K. We can detect density changes of order 10

Secure digital chips such as those found in smart cards are widely used for financial transactions and the transfer of confidential information. Small circuits for high-level information security have to be implemented in these chips. These secure circuits thus require a small ph-RNG (physical random-number generator) capable of generating unpredictable random numbers. A smart card of just a few mm 2 is almost entirely occupied by the CPU, coprocessor, random logic, ROM, RAM, EEPROM, etc., and the memory capacity required is increasing. However, the circuit area of previous ph-RNGs is large, since there is a complex trade-off among circuit area, quality of random numbers and data generation rate. To solve the tradeoff, we use SiN MOSFET as a noise source device, and design a compact A/D converter for SiN MOS-FET RNG. Together these components form a compact ph-RNG circuit as small as 1200μm 2 with a generation rate of 2Mb/s. This ph-RNG circuit area is smaller than one-third of that of any ph-RNG previously reported [1][2][3][4][5], compared at the same generation rate. Furthermore, the quality of random numbers generated by the SiN MOSFET ph-RNG does not depend on temperature, since the origin of random noise signal is a direct tunneling process, theoretically independent of temperature, whereas the origin of random noise in previous ph-RNG is from thermal processes.Previous ph-RNGs are based on thermal noise or thermal carrier injection/ejection in a single or few local traps [1][2][3][4][5]. These noise signals are very small, especially at high frequency, although large noise signals at high frequency are better for a ph-RNG. We use a MOSFET with high-density electron traps in a SiN layer near a Si channel for a noise source ( Fig. 22.8.1). The SiN layer is formed by the same CVD used in the conventional CMOS mass-production process. The SiN MOSFET is fabricated with a CMOS process and one additional photo mask. Electrons are injected/ejected quickly between the Si channel and local traps in SiN layer by direct tunneling. According to electron injection/ejection in many local traps, a large conductance change in the transistor is seen as a large drain current (I d ) fluctuation in the SiN MOSFET. The noise signal of SiN MOSFET is much larger than that of a conventional MOSFET, as shown in Fig. 22.8.1. The circuit blocks for conventional ph-RNG and the SiN MOSFET one are shown in Fig. 22.8.2. Most conventional ph-RNGs require large amplification of the noise signal or a large array of identical noise generators and A/D converters in order to attain over 1Mb/s generation rate, since the noise signals are very small at high frequency. As a result, the amplifier or A/D converter has been very large. In this work, because of the high-amplitude random noise at high frequency from the SiN MOSFET, we need only a single amplifier and A/D converter, and the amplifier area is decreased, as shown in Fig. 22.8.2.In addition to an amplifier and A/D converter, a RNG also needs filters to cut off low-frequency noise origina...

We have formed a micro-texture on a pico-slider’s air-bearing surface to reduce the vibration when the slider comes into contact with the disk. The contact between slider and disk was controlled by adjusting the ‘interference height.’ Our measurements show that, at a giving interference height there is a significant less vibration in the textured slider. This lower amplitude of vibration is attributed to the lower friction force, which is in turn due to the smaller area of contact. We have also introduced the concept of interference area and found that it provides a good explanation of measured vibration.

No abstract

In Greater Tokyo, many people commute by train between the suburbs and downtown Tokyo for 1 to 2 h per day. The spread of influenza in the suburbs of Tokyo should be studied, including the role of commuters and the effect of government policies on the spread of disease. We analyzed the simulated spread of influenza in commuter towns along a suburban railroad, using the individual-based Monte Carlo method, and validated this analysis using surveillance data of the infection in the Tokyo suburbs. This simulation reflects the mechanism of the real spread of influenza in commuter towns. Three measures against the spread of influenza were analyzed: prohibition of traffic, school closure, and vaccination of school children. Prohibition of traffic was not effective after the introduction of influenza into the commuter towns, but, if implemented early, it was somewhat effective in delaying the epidemic. School closure delayed the epidemic and reduced the peak of the disease, but it was not as effective in decreasing the number of infected people. Vaccination of school children decreased the numbers not only of infected children but also of infected adults in the regional communities.