Porter experiments

The process of removing specific spatial frequencies by means of an aperture in the y-plane is called spatial filtering. The effects of spatial filtering on the nature of the image of a simple two-dimensional periodic object will now be illustrated by describing a series of experiments (known as the Porter experiments) and by discussing the observations in terms of the concepts already developed. 

The experimental arrangement for the Porter experiments is shown in Figure 1.10. A small helium-neon laser illuminates an object, which is a 3-mm diameter copper grid of the type commonly used for supporting specimens for transmission electron microscopy. The spacing d between grid bars is 125 /tm. 

So far in this discussion of diffraction, we have assumed that the periodic object is illuminated by coherent light, such as that produced by a small laser of the type used in the Porter experiments. However, the light produced by a thermal source (e.g., a sodium vapor lamp or a heated filament coupled with a narrow bandpass filter) is never strictly monochromatic even the sharpest spectral line has a finite width. Moreover, such a source has finite extent, and the light is emitted by many independent radiators (atoms). These two characteristics of thermal sources are directly related to what are usually referred to as temporal and spatial coherence, respectively. 

J. Rotter, P. Jumikis, S. Flemming and S. Porter. Experiments on the buckling of thin walled model silo structures. J. of Constructional Steel Research, 13 (1989) 271-299. 

Frank Porter Experiences With Generating Workshop Report Using UNIX Jul 24,1992... 

An interferometric method was first used by Porter and Topp [1, 92] to perfonn a time-resolved absorption experiment with a -switched ruby laser in the 1960s. The nonlinear crystal in the autocorrelation apparatus shown in figure B2.T2 is replaced by an absorbing sample, and then tlie transmission of the variably delayed pulse of light is measured as a fiinction of the delay This approach is known today as a pump-probe experiment the first pulse to arrive at the sample transfers (pumps) molecules to an excited energy level and the delayed pulse probes the population (and, possibly, the coherence) so prepared as a fiinction of time. 

Lucas and Porter (U.S. Patent 3,370,401, 1967) developed a fiber-bed scrubber in which the gas and scrubbing liquid flow vertically upward through a fiber bed (Fig. 17-55). The beds tested were composed of knitted structures made from fibers with diameters ranging From 89 to 406 [Lm. Lucas and Porter reported that the fiber-bed scrubber gave substantially higher efficiencies than did venturi-type scrubbers tested with the same dust at the same gas pressure drop. In similar experiments, Semrau (Semrau and Lunn, op. cit.) also found that a fiber-bed contactor made with random-packed steel-wool fibers gave higher efficiencies than an orifice contactor. However, there... 

Irradiation Procedure. Reaction mixtures were prepared at room temperature by transferring desired quantities of reactants from their storage bulbs to the reaction vessel, a 500-cc. spherical borosilicate glass flask attached to the vacuum line by a section of glass capillary tubing and a 4-mm. bore threaded glass valve with a Teflon plug (Fischer and Porter 795-609). Prior to each experiment this vessel was baked under vacuum at 500°C. for 12 or more hours. 

Tanne D, Bates VE, Verro P, Kasner SE, Binder JR, Patel SC, Mansbach HH, Daley S, Schultz LR, Karanjia PN, Scott P, Dayno JM, Vereczkey-Porter K, Benesch C, Book D, Coplin WM, Dulli D, Levine SR. Initial clinical experience with IV tissue plasminogen activator for acute ischemic stroke A multicenter survey. The t-PA Stroke Survey Group. Neurology. 1999 53 424 27. 

If adult odor preferences are in fact influenced by early olfactory experience, then chemosensory processing must be functional early in rodent development. Indeed, the chemosensory systems develop very early in rodents (Alberts 1976 Astic and Saucier 1981), and chemosensory processing appears to be functional both prena-tally (Pedersen and Blass 1982 Stickrod, Kimble and Smotherman 1982) and peri-natally, as evidenced by behavioral responses to odors (Devor and Schneider 1974 Gregory and Bishop 1975 Leon and Moltz 1971 Porter and Etscorn 1974). For example, Syrian hamster pups display behavioral preferences for different types of artificial odorants as early as postnatal day 4 (Devor and Schneider 1974). These data suggest that young rodents are able to both process and respond to odors present in their early environment. 

The extensive research on nitro compounds confirms a rich gas-phase ion chemistry. It is, however, noteworthy that Porter, Beynon and Ast in the classical review, The Modern Mass Spectrometer—A Complete Chemical Laboratory, were able to demonstrate the capabilities of mass spectrometry with no less than thirty different experiments involving a single compound, i.e. nitrobenzene1. 

Figure S.2 shows a schematic diagram of the automatic hydride/vapour-generator system designed by P.S. Analytical. This has been widely used to determine hydrideforming elements, notably arsenic, selenium, bismuth, tellurium and antimony, in a wide range of sample types. To provide a wide range of analyses on a number of matrices the chemistry must be very well defined and consistent. Goulden and Brooksbank s automated continuous-flow system for the determination of selenium in waste water was improved by Dennis and Porter to lower the detection levels and increase relative precision [10, 11]. The system described by Stockwell [9] has been specifically developed in a commercial environment using the experience outlined by Dennis and Porter.

Infants are able to acquire odor preferences on the first day of life. In one experiment, 12 male and 12 female white, healthy, full-term neonates were exposed to the odors of cherry or ginger on a pad taped to the inside of their crib for 24 hours. After this exposure, they were tested for preferences during active sleep (stage II). The behavior was videotaped and the duration of time oriented to each odor measured. Only the female neonates showed a preference for the familiar odor (Balogh and Porter, 1986). Therefore, even on the first day of life, females outperform males, as often described for children and adults (e.g. Yousem etal, 1999). 

Porter and coworkers [98] who have used pc-Au electrodes and have examined monolayers of -alkanethiols CnH2n+lSH with n = 3-10, 12, 16, and 18, have found the surface coverage to be independent of n and equal to 9.3 ( 0.6) xl0 mol cm . Assuming that the real surface area of pc-Au electrode is 1.2 times larger than the geometric surface area, this is consistent with structures proposed on the basis of different experiments in which monolayers of various long-chain n-alkanethiols were found to form a (. 3 X overlayer structure on Au... 

Porter SC, Verseput RV, Cunningham CR. Process optimization using design of experiments. Pharm Technol 1997 21(10) 60-80. 

Porter, Dorothy, and Roy Porter, In Sickness and in Health The British Experience, 16 0-18 0 (1988). 

In a typical experiment, a Fischer Porter 2.5 x 25 cm column containing 55 g of silica gel (70-230 mesh) which had been treated with 2.75 mL of water, was equilibrated with the eluting solvent, hexanes/ethyl acetate (2/1). Five hundred milligrams of the methanolic fraction was adsorbed on 5 g of silica gel and carefully poured on the preequilibrated column. The eluting solvent was then forced (using nitrogen pressure) through the column at the flow rate of 25-35 mL/min and 100 mL fractions were collected. 

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