Dynamics of biexciton localization in AlxGa1-xN mixed crystals under exciton resonant excitation

We report the localization dynamics of biexcitons in AlxGa1−xN mixed crystals under exciton resonant excitation at low temperatures. During a few tens of picoseconds just after intense laser excitation, the photoluminescence (PL) spectral shape obeys an inverse Maxwell–Boltzmann distribution and free biexcitons dominate the PL spectrum. With a further increase in the delay time, the biexciton PL peak energy and edge energy shift to lower energies. These redshift behaviors in AlxGa1−xN mixed crystals are completely different from the behaviors of free biexcitons in GaN crystals. Our observations reveal the rapid transformation dynamics from free to localized biexcitons in band-tail states in AlxGa1−xN mixed crystals

Electromagnetically levitated vibration isolation system for the manufacturing process of silicon monocrystals

This paper introduces a study on an Electromagnetically Levitated Vibration Isolation System (ELVIS) for isolation control of large-scale vibration. This system features no mechanical contact between the isolation table and the installation floor, using a total of four electromagnetic actuators which generate magnetic levitation force in the vertical and horizontal directions. The configuration of the magnet for the vertical direction is designed to prevent any generation of restoring vibratory force in the horizontal direction. The isolation system is set so that vibration control effects due to small earthquakes can be regulated to below 5(gal) versus horizontal vibration levels of the installation floor of up t 25(gal), and those in the horizontal relative displacement of up to 30 (mm) between the floor and levitated isolation table. In particular, studies on the relative displacement between the installation floor and the levitated isolation table have been made for vibration control in the horizontal direction. In case of small-scale earthquakes (Taft wave scaled: max. 25 gal), the present system has been confirmed to achieve a vibration isolation to a level below 5 gal. The vibration transmission ratio of below 1/10 has been achieved versus continuous micro-vibration (approx. one gal) in the horizontal direction on the installation floor

DETC2005-84671 STABILITY-OPTIMIZED CLEARANCE CONFIGURATION OF FLUID-FILM JOURNAL BEARINGS

ABSTRACT A clearance configuration of fluid-film journal bearings is optimized in a sense of enhancing the stability of a full circular bearing at high rotational speeds. A performance index is chosen as the sum of the squared whirl-frequency ratios over a wide range of eccentricity ratios, and a Fourier series is used to represent an arbitrary configuration of fluid-film bearings. An optimization problem is then formulated to find the Fourier coefficients to minimize the index. The whirl-frequency ratio is inversely proportional to the stability threshold speeds of a Jeffcott rotor. The short bearing approximation is used to simplify a mathematical model that describes a pressure distribution developed in a fluid-film bearing. The designed bearing cannot destabilize the Jeffcott rotor at any high rotating speed subject to the short-bearing assumption and significantly reduces the size of the unstable region for a finite-length bearing with a small length-to-diameter ratio

Magnetically Suspended Linear Pulse Motor for Semiconductor Wafer Transfer in Vacuum Chamber

This paper describes a magnetically suspended linear pulse motor for a semiconductor wafer transfer robot in a vacuum chamber. The motor can drive a wafer transfer arm horizontally without mechanical contact. In the construction of the magnetic suspension system, four pairs of linear magnetic bearings for the lift control are used for the guidance control as well. This approach allows us to make the whole motor compact in size and light in weight. The tested motor consists of a double-sided stator and a transfer arm with a width of 50 mm and a total length of 700 mm. The arm, like a ladder in shape, is designed as the floating element with a tooth width of 4 mm (a tooth pitch of 8 mm). The mover mass is limited to about 1.6 kg by adopting such an arm structure, and the ratio of thrust to mover mass reaches to 3.2 N/kg under a broad air gap (1 mm) between the stator teeth and the mover teeth. The performance testing was carried out with a transfer distance less than 450 mm and a transfer speed less than 560 mm/s. The attitude of the arm was well controlled by the linear magnetic bearings with a combined use, and consequently the repeatability on the positioning of the arm reached to about 2 micron. In addition, the positioning accuracy was improved up to about 30 micron through a compensation of the 128-step wave current which was used for the micro-step drive with a step increment of 62.5 micron

Positioning and Microvibration Control by Electromagnets of an Air Spring Vibration Isolation System

Active positioning and microvibration control has been attempted by electromagnets equipped in a bellows-type, air-spring vibration isolation system. Performance tests have been carried out to study the effects. The main components of the system's isolation table were four electromagnetic actuators and controllers. The vibration isolation table was also equipped with six acceleration sensors for detecting microvibration of the table. The electromagnetic actuators were equipped with bellows-type air springs for passive support of the weight of the item placed on the table, with electromagnets for active positioning, as well as for microvibration control, and relative displacement sensors. The controller constituted a relative feedback system for positioning control and an absolute feedback system for vibration isolation control. In the performance test, a 1,490 kg load (net weight of 1,820 kg) was placed on the vibration isolation table, and both the positioning and microvibration control were carried out electromagnetically. Test results revealed that the vibration transmission was reduced by 95%

イリヨウセイ タンスイカブツ ノ キュウヨ ガ ハンスウ ドウブツ ダイ1 イ ナイ キハツセイ シボウサン ノ サンセイ ニ オヨボス エイキョウ IN VITRO シケン ノウガク ブモン

チモシー乾草を朝夕に飽食させている去勢牛より, 給飼前に第1胃より第1胃液を採取した。それを培養液として, まず第1胃内での分解速度の異る炭水化合物を基質として培養を行い, 基質の違いによるVFA産生状況, また尿素添加によるVFA産生状況の変化について調べた。その結果, 分解速度の速い基質ほどVFA産生量は多く, VFA産生割合は酢酸が低くプロピオン酸, 酪酸が増加した。尿素添加によってpHは上昇し, アンモニアが多量に産生された。次に基質として小麦粉を用いて同様の培養試験を行い, 基質の多小および煮沸処理, また尿素添加によるVFA産生状況の変化について調べた。その結果基質量の多いほどVFA産生は多く, VFA産生割合は酢酸で小さく, プロピオン酸, 酪酸で大きかった。煮沸処理によりその傾向は強められた。尿素添加の影響は第1試験と同様であった。最後に培養液として飼料給与後3時間目に採取した第1胃液を用い, 小麦粉を基質として培養試験を行いVFA産生状況を調べた。その結果, 基質添加によってVFA産生は多くなるがその値は煮沸処理により低くなり第2試験とは逆の傾向を示した。尿素を添加した場合は無処理よりも煮沸した場合の方がVFA産生量は高かった。VFA組成は基質添加によって酢酸は小さく, プロピオン酸は大きくなったが, 煮沸処理によって無処理より酢酸では大きく, プロピオン酸では小さくなった。尿素添加によって煮沸したものと無処理のものの差はほとんど無くなった。尿素添加によってアンモニア産生量は増加したが, 第1・第2試験ほどでは無かった。Rumen liquid collected from fisturated steer before feeding was used as culture solution. In the first place, incubation was carried out with substrates which were different in availability to examine the effect of availability of substrate on VFA production. The more available substrate produced the higher VFA concentration, the lower molar proportion of acetic acid and the higher molar proportions of propionic and butyric acids. Secondly, wheat flour was used as substrate to examine the effect of the amount of substrate on VFA production. The more amount of substrate produced the high VFA concentration, the lower molar proportion of acetic acid and the higher molar proportions of propionic and butyric acids. These trends were strengthened by cooking of wheat flour. Lastly, the rumen liquid which was collected three hours after feeding was used as culture solution. Similar results were obtained as in the second incubation in VFA production. The molar proportion of acetic acid was decreased by cooking of wheat flour, however, this trend disappeared following urea addition

Ultrafast decay of photoluminescence from high-density excitons in Al_{x}Ga_{1−x}N mixed crystals: Diffusive propagation of exciton-polaritons

We report on the ultrafast decay dynamics of photoluminescence (PL) in highly excited AlxGa1−xN mixed crystals under exciton resonant excitation at low temperatures. When the excitation intensity is increased, the P-band emission appears due to exciton-exciton inelastic scattering processes. The PL intensity of the P band decays rapidly, with a much shorter decay time than the radiative recombination time of the excitons. We show that the ultrafast PL decay dynamics can be understood as due to the disorder-induced diffusive propagation of photonlike exciton-polaritons in AlxGa1−xN mixed crystals

Composition dependent dynamics of biexciton localization in AlxGa1-xN mixed crystals

We report the localization-dependent dynamics of biexcitons in AlxGa1−xN mixed crystals under exciton resonant excitation at low temperatures. After intense laser excitation, biexcitons rapidly localize into the band-tail states. The formation time of localized biexcitons becomes shorter with increasing Al composition. Both the inhomogeneous linewidth and the binding energy of biexcitons increase with the inhomogeneous linewidth of excitons. The biexciton binding energy is enhanced by the restriction of exciton motion to disordered potentials and the dynamics of stable biexcitons determines the optical spectrum in mixed crystals