Time focussing

Mills (1984) pointed out that it might soon be experimentally feasible to realize systems containing positrons which overlapped one with another, both spatially and temporally. This was due to the production of time-focussed beams and the prospects (since demonstrated) for brightness-enhanced, highly focussed beams. 

More and more patients seek advice on complementary medicine via the Internet. It is therefore important to monitor the validity of such advice. In one survey, most of the 13 most popular websites on complementary medicine for cancer recommended cancer therapies for which there was no evidence of efficacy (30). Three of the sites overtly discouraged cancer patients from using conventional therapies. When the study was repeated, this time focussing on HIV instead of cancer, the results were virtually identical (31). These findings were similar to those of another study of 61 popular websites on herbal medicines for cancer (32). Most of these sites were commercial by nature and claimed cancer cures through herbal medicines, with little regard for current regulations. 

In this Appendix we derive the analytical expression for the energy resolution of a low-bandpass spectrometer like TOSCA ( 3.1) (also known as crystal analyser spectrometers) and describe two key features of the design ( 3.2), time focussing ( 3.2.1) and the Marx principle ( 3.2.2) that improve the resolution at high and low energy transfer respectively. 

Time focussing was first introduced in the LAM-D spectrometer at KENS [1] and has been adopted in all subsequent crystal analyser instruments. The key feature is that the planes of the sample, analyser and detector are parallel as shown in Fig. A3.1. For simplicity, a point sample is assumed. From Fig A3.1 for the ray shown by the solid line it can be seen that the length of the final flight path from sample to detector, df, is given by ... 

Note that the Marx principle is more restrictive than time focussing in the latter all that is necessary is that the sample, analyser and detector planes are parallel, in the former the planes must not only be parallel but the sample and detector planes must also be co-planar. Time and energy focussing are so successfiil that all current and planned crystal analyser spectrometers employ it. The only exception is the forward scattering bank on TOSCA where limitations on space meant that the detectors were placed slightly downstream from the sample plane. In practice, the displacement is small enough that the resolution is essentially the same in both the forward and backscattering detector banks. 

Small scale test runs prior to preparative irradiation experiments may be carried out in tubes which are either taped to the lamp housings (immersion wells) depicted in Figures 13-1 and 13-2 or placed in turntable reactors ( merry-go-rounds ). These arrangements permit the simultaneous irradiation of several samples, but only a fraction of the available light emission is used. In Figure 13-4 a simple reactor is shown which focusses almost all the emitted light into one sample which can be scaled up also to semi-preparative volumes. In this way the necessary irradiation time can be reduced sharply. 

Besides the classical search for linear, one-dimensional electronically active materials, synthetic approaches are now also focussed on the generation and characterization of two- and three-dimensional structures, especially shape-persistent molecules with a well-defined size and geometry on a nanometer-scale. It is therefore timely and adequate to extend concepts of materials synthesis and processing to meet the needs defined by nanochcmislry since the latter is now emerging as a subdiscipline of material sciences. 

Although an efficient reaction, the Rees-Atkinson aziridination method suffers from two drawbacks the necessity for an N-phthalimido or N-quinazolinonyl substituent and the use of a highly toxic oxidant. Thus, recent efforts (especially in these green times) have focussed upon more benign methods for generation of the key nitrenoids. Yudin demonstrated the power of electrochemistry with a novel method that removes the need for an added metal oxidant, demonstrating an unusually and impressively broad substrate tolerance compared to many alkene aziridination reactions (Scheme 4.14) [10]. 

Abstract Polysaccharides from plants have been the subject of studies for a very long time, mainly focussed on their physical properties, their chemical and physical modification, and their application. Over the last 20 years there has heen increasing interest... 

In 1996, we started more detailed investigations on group 13/15 compounds containing the heavier elements of group 15, Sb and Bi, focussing on the synthesis of aluminum and gallium stibines and bismuthines. At the same time. Wells et al. also began to prepare M—Sb adducts and heterocycles (M = B, Ga, In). These studies, which are the object of this review, resulted in... 

Only one nncleophile particle and only one alkyl halide molecule One bond broken and one bond formed Leaving aside the implication of intent on the part of the nncleophile (rather than a probabihstic view of the event), this extract wonld be acceptable if it were explicitly stated that it focussed on just one of the veiy many reaction events that occurred at various points in time in the reaction mixtnre. 

Study of the recoil chemistry of organometallic compounds for its own sake, began really in 1955 with the publication of a study (56) by Mad-dock and Sutin on neutron activation of triphenylarsene. Since this time, most of the published work has been focussed on those radioactive atoms which did not permanently escape their ligands. Thus, in one way or another, they end up in molecular form. It is with these that this review is largely concerned. 

The nature of the solidification process in these cements has received little attention. Rather, attention has focussed on the crystalline components that form in cements which have been allowed to equilibrate for some considerable time the nature of such phases is now quite well understood. Gelation is reasonably rapid for these cements and occurs within a significantly shorter time than does development of crystalline phases. The conclusion may be drawn that initial cementition is not the same as crystallization, but must occur with the development of an essentially amorphous phase. Reactions can continue in the amorphous gelled phase, but are presumably limited in speed by the low diffusion rates possible through such a structure. However, reactions are able to proceed substantially to completion, since in many cases X-ray diffraction has demonstrated almost quantitative conversion of the parent compounds to complex crystalline mixed salts, though several days or weeks of equilibration are required to bring this about. 

The output of a Nd YLF laser is focussed by a series of lenses to a spot size of 0.5 pm upon a sample which may be positioned by an x-y-z stepping motor stage and scanned by a computer-controlled high frequency x-y-z piezo stage. Ions are accelerated and transmitted through the central bore of the objective into a time-of-flight (TOF) mass spectrometer. The laser scans an area of 100 x 100 pm with a minimum step size of 0.25 pm. TOF mass spectra of each pixel are evaluated with respect to several ion signals and transformed into two-dimensional ion distribution plots. 

The structure-activity considerations at that time naturally enough focussed interest on epoxides formed at the K-regions of the carcinogenic hydrocarbons (Figure 3), but it was not until 1964 that the synthesis of such putative metabolites was achieved (46). 

To compare different profiles, peaks were matched by their retention times and mass spectra. The contribution of each peak to the overall area of the profile was calculated as a percentage (% area) and used for analyses. For the current study we focussed our analyses on fatty acids and esters (Poddar-Sarkar and Brahmachary 1999 Hofer et al. 2001). 

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