Interference experiments

Good agreement is reported to exist between the Dugdale plastic zone model and optical interference experiments, performed at the tip of a crack. Morgan and Ward [79], Fraser and Ward [80] and more recently and extensively Doll and... 

Young s Interference Experiment (1.5) A Young s interferometer basically consists of a stop with two holes ( array elements ), illuminated by a distant point source, and a screen which picks up the light at a sufficiently large distance behind the holes. The light patch produced by the stop is extended and shows a set of dark fringes which are oriented perpendicularly to the direction which connects the centers of the two openings. 

That light has a dual nature and behaves either like a wave or like a stream of particle-like photons is a fact we must accept, although it is nonintuitive. But remember, we have no direct experience of the behavior of very small particles such as electrons. Which model we use depends on the observations we are making. The wave model is appropriate when we are considering diffraction and interference experiments, but the particle (photon) model is essential when we are considering the interaction of light with individual atoms or molecules. 

The needle-shaped wavepacket solutions of the individual photon model, which agree at least sometimes with the dot-shaped marks on a screen in interference experiments... 

These questions appear to be understandable in terms of both photon models. The wavepacket axisymmetric model has, however, an advantage of being more reconcilable with the dot-shaped marks finally formed by an individual photon impact on the screen of an interference experiment. If the photon would have been a plane wave just before the impact, it would then have to convert itself during the flight into a wavepacket of small radial dimensions, and this becomes a less understandable behavior from a simple physical point of view. Then it is also difficult to conceive how a single photon with angular momentum (spin) could be a plane wave, without spin and with the energy hv spread over an infinite volume. Moreover, with the plane-wave concept, each individual photon would be expected to create a continuous but weak interference pattern that is spread all over the screen, and not a pattern of dot-shaped impacts. 

A. Kyprianidis and J. P. Vigier, Quantum properties of chaotic light in first order interference experiments, Europhys. Lett. 3(7), 771-775 (1987). 

Whenever light produces an observable effect, for example, when it acts on a photographic plate or knocks an electron out of an atom, it appears to act like particles. In interference experiments it is not the waves which are observed, but the distribution of light intensity. This is done by means of a photographic plate, or in some other equivalent way. The observed distribution of intensity is thus not a distribution of waves but a distribution of photons, or rather a distribution of effects attributed to photons. The photons themselves are not observed any more than the waves are. 

Consider Wiener s interference experiment shown in Fig. 11 on the particle theory. On this theory we have photons moving towards the mirror, which bounce off from it and come back. These photons pass through the photographic film as they move towards the mirror, and as they come back. If a photon hits a grain of silver bromide in the film, it is absorbed by the grain and so disappears. It is clear that the plate should be uniformly affected all over and not show the bands which are actually observed. In the bands, however, only some of the grains are affected, which cannot be explained on the wave theory. It is clear that what is required is some sort of combination of the two theories. This will be considered in the next chapter. 

If, instead of one hole in the plate P, there are two narrow slits close together, we have a Young s interference experiment, and the intensity of the waves will not be uniform on the plates, but will be distributed in narrow bands as we have seen. In this case the particle will be certain to fall in one of the bands, and not in between two bands. 

Radial distribution functions can be determined experimentally using diffraction (i.e., interference) experiments. X-rays or neutrons can be used. If one knows the pair correlation function g ir) for each atom, one can work out the short-range structure in a liquid. The question is then how does one find gj ir) ... 

Fullerenes and their derivatives not only represent the most massive and most complex single particles in interference experiments until recently, they also mark a qualitative step towards the mesoscopic world. In many aspects they resemble rather small solids than simple quantum systems they possess collective many-particle states like plasmons and excitons, and they exhibit thermionic electron, photon and particle emission [Mitzner 1995 Hansen 1998] - which may be regarded as microscopic analogs of glow emission, blackbody radiation and thermal evaporation. Fullerenes contain about two... 

The model Hamiltonian of Section II captures some of the essential features of the electronic and vibrational structure of polyatomic molecules, like benzene and 5ym-triazine, that have both nondegenerate and degenerate, Jahn-Teller active, electronic levels. In this section interference experiments are described which will be sensitive to the geometric phase development accompanying adiabatic nuclear motion on either of the electronic potential energy surfaces in the Jahn-Teller pair. 

We hope that the studies summarized above will motivate time-resolved interference experiments on Jahn-Teller systems. Half-odd quantum numbers for molecular pseudorotation have been reported in the continuous wave spectra of Na, [47], benzene [48] and sym-triazine [44]. The half-odd quantum numbers are strong evidence for the presence of geometric phase factors. Benzene and sym-triazine have nondegenerate ground states and would therefore be the most obvious choices for phase sensitive measurements of the kind we propose. The 3s E Rydberg state of 5ym-triazine has the simplifying feature of exhibiting Jahn-Teller... 

A schematic diagram of an interference experiment of the Young type is shown in Fig. 1. Two light beams of amplitudes Ei(ri,fi) and E2(r2,f2) produced at two slits Si and S2 located at ri and r2, respectively, incident on the screen at a point P. The resulting field detected at the point P is a linear superposition of the two fields... 

Random incorporation of modified residues in in vitro transcribed RNA is of particular interest in analogue interference experiments (Section 4.6.3) where randomly modified RNA molecules with altered properties are selected and compared to the original pool of RNA molecules. A crucial prerequisite for the interference analysis is the ability to identify the modified residues. A convenient and efficient method is the use of nucleotides which contain both the modification of interest (e.g. 2 -0-methyl NTP, dNTP, inosinetri-phosphates) and an a-phosphorothioate group (one of the nonbridging oxygens is replaced with a sulphur).14-16 The concurrent incorporation of the phosphorothioate renders the modified nucleotides sensitive to a selective cleavage by iodine. 

The basis of a modification interference experiment is an initial modification followed by a selection procedure, where RNA molecules that retain their normal properties with respect to the selection procedure are separated from molecules with altered properties (e.g. modified RNA molecules that still bind a protein can be separated from modified RNA molecules that are unable to bind the protein see Fig. 4.15). 

Hydrazine, CMCT, kethoxal, DMS and DEP (described in Section 4.3.2) are useful for modification interference experiments. Procedures in Section 4.4.2 can be adopted directly for modifications under native conditions, while the procedures used for chemical sequencing of RNA (Section 4.4.3.2.2) generally produce a uniformly modified RNA at denaturing conditions. 

Each factor contributes to a final score, and the siRNAs with higher scores are predicted to be better than lower-scoring siRNAs. The determination of these characteristics suggested the usefulness of rational design of potent siRNAs for RNA interference experiments. 

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