SPIDER technique

The FROG method provides information on the time-dependent frequency spectrum of a short pulse but cannot measure the phases of these spectral components. A newly developed technique is helpful in this case this method is called SPIDER (Spectral Phase /nterferometry for Direct Field Reconstruction). It uses the interference structure generated when two spatially separated pulses are superimposed [788]. Similar to the autocorrelation method, the two pulses are generated from the input pulse that is to be measured, using a beam splitter and a delay line which changes the time delay between the two pulses. The second pulse is therefore a copy of the first pulse with a time delay t. The electric field amplitude 

The intensity measurement at the location x is therefore related to the phase difference A4 = 4 x) - 4 (x + Ax) between the phases of the wavefront at the locations 

The principle of this method is depected in Fig. 6.85. The signal pulse at the frequency co and its frequency-shifted replica 2A(o + Sa pass with a time delay x through a beam of noble gas atoms. The high harmonics at and n( w -j- Sw) are diffracted by a concave grating and reach the detector. 

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There are two different techniques that are used to measure the time profiles and optical oscillations of ultrashort pulses noncoUinear intensity correlation and interferometric autocorrelation. While the former measures the envelope of the pulse, the latter can even measure the optical oscillations within the pulse envelope. Combined with the spectral resolution, the time profiles of the different spectral components within the optical pulse spectrum can be simultaneously measured by the FROG technique. The relative phases of these spectral components are observable using the SPIDER technique (see Sect. 6.2.4). 

This signal is measured behind a spectrograph as a function of the delay At between pulses 1 and 2. The measured frequency shift i2 = Ar of the sum frequency gives the phase < (r) of the unknown input pulse and its time profile I(t). Figure 6.81 illustrates the principle of the SPIDER technique using a schematic diagram. 

Chemists teamed the basic composition of siik many years ago, but the reasons why this macromoiecuie is so strong, yet fiexibie, are stiii not fuiiy understood. Recent studies indicate that the secret ties in the way the chains of this protein nestie together. Current research efforts focus on using techniques of genetic engineering to repiicate naturai spider siik on a usefui scaie. 

Because of the small amounts of sample that are usually obtained, coupled GC-MS is the method of choice for analysis of volatile pheromones. The analysis of the less-volatile lipids and polar pheromone components may require derivatization and microchemical tests, both to improve chromatographic characteristics and to provide information about the structures. It is likely that chromatographic techniques with high separation power and high sensitivity for polar compounds, such as coupled capillary electrophoresis-mass spectrometry, will prove useful for analysis of spider extracts in future studies. 

Nevertheless, silk spinning remains a very complex process. Spiders and silkworms not only have a set of well-developed spinning glands but also have a set of well-defined and controlled chemical boundary conditions. Besides the composition of the spinning dope, the spinning techniques and the combination of chemical parameters (pH and metallic ions) must be considered and optimized. 

Coextrusion can be performed with flat, tubular, and different shaped dies. The simplest application is to nest mandrels and support them with spiders or supply the plastic through circular manifolds and/or multiple ports. Up to 8-layer spiral mandrel blown film dies have been built that require eight separate spiral flow passages with the attendant problem of structural rigidity, interlayer temperature control, gauge control, and cleaning. Many techniques are available for coextrusion, some of them patented and available under license (Chapter 5). 

Organic growers also use biological control. They are allowed to import natural enemies of pests. This works either through predation or parasitism. This has proven effective for the control of red spider mite and specific caterpillars, and does not affect other insects. And a third technique is to use insect traps ranging from sticky yellow strips to pheromone or sexual lures. The pheromone traps use synthetic extracts of the chemical scents that... 

Mites, ticks, spiders, sowbugs, pillbugs, centipedes, and millipedes resemble insects in size, shape, life cycle, and habits. Pest species usually can be controlled with the same techniques and materials used to control insects. 

The spider diagram technique (p. 326) is a speedy way of doing this. If you have time to read several sources, consider their content in relation to the essay title. Can you spot different approaches to the same subject Which do you prefer as a means of treating the topic in relation to your title Which examples are most relevant to your case, and why ... 

Many controversial techniques have been employed in the management of true Brown Recluse spider bites. Unfortunately, no scientific evidence exists which supports an ideal method or methods of management. However, case reports advocate a variety of therapies as potentially useful. Most agree, however, that good local management of the cutaneous lesion is the most important aspect of care. Tetanus prophylaxis should always be included. In... 

Figure 13(b) shows a JH—15N HSQC spectrum acquired from 0.5 mmol l-1 sample of a 41-residue peptide toxin from the spider Agelena orientalis. The toxin was produced recombinantly and uniformly labeled with 15N. This HSQC spectrum was collected in 30 min, compared with the 12 h required to acquire a natural abundance spectrum from an unlabeled sample of equivalent concentration (see Figure 11). The HSQC, together with the related heteronuclear multiple quantum coherence (HMQC)54 experiment, forms the cornerstone of a wide range of 2D, 3D, and 4D experiments that are designed to facilitate sequence-specific resonance assignment and determination of protein structure. Note that the HSQC technique is the technique of choice for correlation of H and 15N shifts due to generally narrower linewidths in the 15N dimension.55,56 Furthermore, because these and most of the other heteronuclear experiments described below are designed to observe amide protons, the sample must be in H20 (rather than D20). Consequently, a means of suppressing the H20 resonance is required (for details see Section 9.09.2.6).

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