Despite the long-standing importance of transient absorption (TA) spectroscopy, many researchers remain frustrated by the difficulty of measuring the nanosecond range in a wide spectral range. To address this shortcoming, we propose a TA spectrophotometer in which there is no synchronization between a pump pulse and a train of multiple probe pulses from a picosecond supercontinuum light source, termed the randomly-interleaved-pulse-train (RIPT) method. For each pump pulse, many monochromatized probe pulses impinge upon the sample, and the associated pump-probe time delays are determined passively shot by shot with subnanosecond accuracy. By repeatedly pumping with automatically varying time delays, a TA temporal profile that covers a wide dynamic range from subnanosecond to milliseconds is simultaneously obtained. By scanning wavelength, this single, simple apparatus acquires not only wide time range TA profiles, but also broadband TA spectra from the visible through the near-infrared regions. Furthermore, we present a typical result to demonstrate how the RIPT method may be used to correct for fluorescence, which often pollutes TA curves.

Attenuated total reflectance (ATR)-FTIR spectroscopy has been widely used to probe protein structural changes under various stimuli, such as light absorption, voltage change, and ligand binding, in aqueous conditions. Time-resolved measurements require a trigger, which can be controlled electronically; therefore, light and voltage changes are suitable. Here we developed a novel, rapid buffer-exchange system for time-resolved ATR-FTIR spectroscopy to monitor the ligand- or ion-binding re-action of a protein. By using the step-scan mode (time resolution; 2.5 ms), we confirmed the completion of the buffer-exchange reaction within ∼25 ms; the process was monitored by the infrared absorption change of a nitrate band at 1,350 cm−1. We also demonstrated the anion-binding reaction of a membrane protein, Natronomonas pharaonis halorhodopsin (pHR), which binds a chloride ion in the initial anion-binding site near the retinal chromophore. The formation of chloride- or nitrate-bound pHR was confirmed by an increase of the retinal absorption band at 1,528 cm−1. It also should be noted that low sample consumption (∼1 µg of protein) makes this new method a powerful technique to understand ligand–protein and ion–protein interactions, particularly for membrane proteins.

IutroductionHiFD is the floppy disk which combines a 200MB capacity with full downward compatibility with conventional 3.5" FD [I]. The technology of hard disk is moving toward pseudo-contact remrding and the flying height has been reduced [2]. On the other hand, conventional 3.5" FD is contact recording. HiFD system tries to achieve pseudo-contact recording by increasing the rotation speed to 3600rpm. Numerous studies have been pursued to examine head-disk interface (HDI) of hard disk. There were, however, few studies of HDI of floppy disk under high rotation speed. In this paper, we discuss the friction force between the head and the floppy disk under high rotation speed from a viewpoint of the amount of lubricant on the disk.Exoerimental m e disk was 3.5" particulate recording disk which has magnetic upper layers (0.2nm) and nonmagnetic under layers (1.5um) on botb sides of PET (62bt1). The-surfaie roughnes-Ra of the disk was approximately 4nm. Alkyl carboxylate was incorporated as lubricant into the disk-A. Moreover, it was coated by the spin-coater with concentration of 5 and 8 wt% toluene solution on the disk-A, respectively (disk-B and disk-C). The friction force was measured by the difference in the motor current before and after the head loading. Relative friction force was normalized by the value of the diskB at 13.2 m/s. Relative velocity was changed by the disk rotation speed while head position has been kept.Results and Dlscussion Figure 1 shows relative velocity dependence of friction force as coating lubricant on the disk-A. Friction force of disk-A decreased with increasing relative velocity. Friction force of diskB was steady in low value when relative velocity was faster than 4.4m/s. The friction of the disk-C was always higher than that of the disk-B. In less than 4.4m/s, the relative friction force exceeded 22 and the head began to creak. Figure 2 shows friction force of 13.2ds versus concentration of the applied toluene solution with the lubricant. The friction force decreased gradually with concentration, and increased rapidly in the concentration around the 8wt%. The amount of surface lubricant will be discussed.From these results, applying lubricant to the disk-A, the friction force decreases gradually and is steady in a low value over a certain relative velocity, that is, the condition of head flying is almost reached. However, as the lubricant exceeds a proper amount, the contact between the head and the disk occurs again. It is considered that it is due to the appearance of the meniscus by excess lubricant. Magn. Magn.Mater., to be published. 0 0 2.2 4.4 6.6 R d I1 1 3 2 15.4 ( -1 ( I l m r n )

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