Pre-bunching

These single-pulse, picosecond electron linacs employed a method called sub-harmonic pre-bunching (Fig. 1) to create a... 

Fig. 1. Schematic representation of a pre-bunched picosecond linear accelerator.

Because it involves more accelerating structures with multiple RF frequencies and phase relationships, and a high-performance electron gun source to inject the electrons in about one nanosecond, a sub-harmonic pre-buncher adds a lot of cost and complexity of operation ofthe linac facility. Consequently, only a few pre-bunched picosecond linacs were built for pulse radiolysis studies. The first one was installed at Argonne National Laboratory in the 1970s [2] subsequently other picosecond installations were built at the University of Tokyo Nuclear Energy Research Laboratory (NERL) in Tokai-Mura [3,4] and Osaka University [4].Very recently, a new pre-bunched linacfor pulse radiolysis has been built at the Shanghai Institute of Applied Physics. 

Photocathode-based picosecond electron accelerators are conceptually simpler than pre-bunched thermionic systems, although they require reasonably powerful, multicomponent femtosecond or picosecond laser systems to drive the photocathode. In addition, the availability of synchronized laser pulses allows the development of advanced detection capabilities with unprecedented time resolution. The combination of ease of use and powerful detection methods has stimulated strong interest in photocathode gun systems. Since the installation ofthe first photocathode electron gun pulse radiolysis system at BNL [5,13], four additional photocathode-based facilities have become operational and two more are in progress. The operational centers include the ELYSE facility at the Universite de Paris-Sud XI in Orsay, France [7,8], NERL in Tokai-Mura, Japan [9,10], Osaka University [11,12], and Waseda University in Tokyo [13]. Facilities under development are located at the Technical University of Delft, the Netherlands, and the BARC in Mumbai, India. 

Although Pasteur was unable to provide a structural explanation—that had to wait for van t Hoff and Le Bel a quarter of a century later—he correctly deduced that the enantiomeric quality of the crystals was the result of enantiomeric molecules The rare form of tartanc acid was optically inactive because it contained equal amounts of (+) tartaric acid and (—) tartaric acid It had earlier been called racemic acid (from Latin racemus meaning a bunch of grapes ) a name that subsequently gave rise to our pres ent term for an equal mixture of enantiomers... 

Both traps have been tested and perform almost as specified (ratio of incoming to ejected ion intensity about 10" for the bunching trap, resolution of the pre-cision trap = 3.10 for A = 28). The transfer of the ions from the bunching trap to the precision trap is now under study. 

Four principal models have been proposed to explain the presence of alteration phases in chondritic meteorites. These models can be summarized as follows (i) reaction of anhydrous, high-temperature condensate phases with water vapor as the solar nebula cooled to temperatures below —375 K (e.g., Grossman and Larimer, 1974]) (ii) hydration of anhydrous dust in icy regions of the nebula during the passage of shock waves (Ciesla et al., 2003) (iii) alteration within small (tens of meters), ephemeral parent bodies that were subsequently disrupted and their altered components accreted with unaltered materials into the final asteroidal parent bodies (pre-accretionary alteration) (Metzler et al., 1992 Bischoff, 1998) and (iv) alteration within asteroidal parent bodies (Kerridge and Bunch, 1979 Zolensky and McSween, 1988). 

These data suggest that alteration of the Cl chondrites took place over an extended timescale, indicating an asteroidal environment for alteration (Hutcheon, 1997). Given that early-formed magnetite is almost certainly the product of aqueous activity (e.g., Kerridge and Bunch, 1979), alteration probably occurred, almost entirely, within an asteroidal environment. It is possible that precursor components of the Cl chondrites experienced pre-accretionary alteration (Bischoff, 1998). However, it is clear that... 

Yunus, R., Salleh, S. F., Abdullah, N., Biak, D. R. A. Effect of ultrasonic pre-treatment on low temperature acid hydrolysis of oil palm empty fruit bunch. Bioresource Technology 2010,101,9792-9796. 

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