Effects of Pulses

A pulse is a burst of radiofrequency energy that may be applied by switching on the Rf transmitter. As long as the pulse is on, a constant force is exerted on the sample magnetization, causing it to precess about the Rf vector. 

We can control the extent by which the -l-z-magnetization is bent by choosing the duration for which the pulse is applied. Thus the term 90° pulse actually refers to the time period for which the pulse has to be applied to bend the magnetization by 90°. If it takes, say, t p-s to bend a pulse by 90°, it would require half that time to bend the magnetization by 45°, i.e., t/2 ps. A 180° pulse, on the other hand, will require double that time, i.e., 2t ps and cause the z-magnetization to become inverted so that it comes 

The bandwidth is inversely proportional to the pulse duration. Following is a computer simulation of a short pulse (left) and its calculated 

As stated earlier, when placed in a magnetic field, the bulk magnetization of the nuclei will precess about the applied magnetic field with a 

Based on the right-hand thumb rule described in the text, and assuming that only an equilibrium magnetization directed along the z-axis exists, draw the positions of the magnetization vectors after the application of  

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FIG. 15 53 Effect of pulsing on extraction in a packed column methyl isobutyl ketone-acetic acid-water (continuous). Tower diameter = 1.58 in, 27-in depth of V4-in Raschig rings. = Vc = 7.5 to 10. To convert inches to centimeters, multiply by 2.54. [Data of Chanhy, von Berg, and Wiegandt, Ind. Eng. Chem., 47, 1153 (1.9.55), with permission. ... 

Table 8-2 contains unpublished results fron the authors laboratory that illustrate the effectiveness of pulse-height selection in the determination of light elements. In the case of silicon, the background was due mainly to scattered x-rays. In the case of sulfur, multiplier phototube noise was also present. The counting interval was 10 seconds for Nt (total count) and for Nb (background). The excellent results for sulfur could not have been obtained had there not been careful and fortunate selection of the multiplier phototube. 

Table 8-2. Effectiveness of Pulse-Height Selection (PHS) in Reducing Background...

Stellwagen, NC, Effect of Pulsed and Reversing Electric Eields on the Orientation of Linear and Supercoiled DNA Molecules in Agarose Gels, Biochemistry 27, 6417, 1988. 

In the interdisciplinary field of biophysics and biotechnology, the bioeffects of electric field have received considerable interest for both fundamental studies on these interaction mechanisms and potential application. However, the effects of pulsed electric field (PEF) on secondary metabolism in plant cell cultures and fermentation processes have been unknown. Therefore, it would be very interesting to find out whether PEF could be used as a new tool for stimulating secondary metabolism in plant cell cultures for potential application to the value-added plant-specific secondary metabolite production. Furthermore, if the PEF permeabilization and elicitation are discovered in a cell culture system, the combination of... 

The effect of pulses on magnetization vectors is much easier to understand in the rotating frame than in the fixed frame. How do we arrive at the chemical-shift frequencies in the rotating frame ... 

Figure 2.9 Pulse sequence for the INEPT experiment. (B) Effect of pulses on H magnetization. Application of the pulse sequence shown results in population inversion of one of the two proton vectors of the CH doublet and therefore causes an intensification of the corresponding C lines.

Soliva-Fortuny, R. C., Balasa, A., Knorr, D., and Martin-Belloso, O. (2009). Effects of pulsed electric fields on bioactives compounds in foods A review. Trends Food Sci. Technol. 20, 544-556. 

Zhao W, Yang R, Wang M and Lu R. 2009. Effects of pulsed electric fields on bioactive components, colour and flavour of green tea infusions. Int J Food Sci Technol 44 312-321. 

THORNTON, J. D. Trans. Inst. Chem. Eng. 35 (1957) 316. Liquid-liquid extraction. Part XIII. The effect of pulse wave-form and plate geometry on the performance and throughput of a pulsed column. 

Picosecond spectroscopy was performed using an apparatus described by Reynolds and Rentzepis (9 ). The duration of the excitation pulse was 25 psec at 530 nm. Pulse intensity was about 1.5 m joules. Dependence of relaxation time on power from 0.3 up to 2.0 m joules revealed no effects of pulse intensity on decay times. 

Tang, S., Krasieva, T. B., Chen, Z., Tempea, G., and Tromberg, B. J. 2006. Effect of pulse duration on two-photon excited flourescence and second harmonic generation in nonlinear optical microscopy./. Biomed. Opt. 11 020501. 

In Reference [43], the effect of pulse-shape has been also addressed by applying to a 30 fs pulse a quadratic phase chirp whose group delay dispersion is 630 fs, thereby stretching the pulse-duration to 120 fs. The dominant ro-vibrational states in this PD process by a 795nm laser are the Vj = 9, = 3 states (states with = 3... 

Pulsed-current techniques can furnish electrochemical kinetic information and have been used at the RDE. With a pulse duration of 10-4 s and a cycle time of 10-3 s, good agreement was found with steady-state results [144] for the kinetic determination of the ferri-ferrocyanide system [260, 261], Reduction of the pulse duration and cycle time would allow the measurement of larger rate constants. Kinetic parameter extraction has also been discussed for first-order irreversible reactions with two-step cathodic current pulses [262], A generalised theory describing the effect of pulsed current electrolysis on current—potential relations has appeared [263],... 

Studies on the effect of pulsed nuclear reactor irradiation were conducted on RD-1333 Pb azide (Ref 254). Bulk samples of RD-1333 were exposed to a total dose of 2.0 x 1014 n/cm2 from an unmoderated, unreflected, prompt pulsed reactor in a pulse 40 to 50 psec full-width at half-maximum. Analyses of the Pb azide which included the vacuum stability test, expln temp test, and the detonation velocity test, did not show any changes due to the transient radiation environment... 

In products of two operators, each one evolves independently also under the effect of pulses. For instance ... 

Among the adverse effects of pulse glucocorticoid therapy, joint manifestations are rare. A woman with systemic lupus erythematosus and nephritis developed transient bilateral knee effusions during pulse therapy with high doses of glucocorticoids (279). 

Lee, H.-J., Moon, S.-H., and Tsai, S.-P. 2002b. Effects of pulsed electric fields on membrane fouling in electrodialysis of NaCl solution containing humate. Sep. Purif. Technol. 27, 89-95. 

Naddy, R.B. and Klaine, S.J. (2001) Effect of pulse frequency and interval on the toxicity of chlorpyrifos to Daphnia magna, Chemosphere 45 (4-5), 497-506. 

Figure 5. Effects of pulse length on wideline NMR spectra of aluminosilicate gels containing (a) 5% V, 7/ s pulse length, resulting in exclusive detection of bulk Vp05 (b) 3% V, 7/ s pulse length, resulting in exclusive detection of amorphous V Oj-and (c) 3% V, 1/xs pulse length, resulting in a spectrum representative of all V+D species present.

Dusenbery, D. B. (1989) Calculated effect of pulsed pheromone release on range of attraction. J. Chem, Ecol. 15, 971-977. 

Heming TA, McGuinness EJ, George LM, Blumhagen KA. 1988. Effects of pulsed- and spiked-exposure to methoxychlor on early life stages of rainbow trout. Bull Environ Contain Toxicol 40 764-770. 

Kersting K, van Wijngaarden RPA. 1999. Effects of pulsed treatment with the herbicide afa-lon (active ingredient linuron) on macrophyte dominated mesocosms I. Resonses of ecosysem metabolism. Environ Toxicol Chem 18 2859-2865. 

The effect of pulses is very simple each individual operator is acted on by the pulse, and replaced by the result of that rotation about the Bi vector. For example, consider the effect of a 90° XH pulse on the x axis ... 

For example, — 2IbI is read as proton Hb net magnetization on the — x axis, antiphase with respect to its coupling partner Ha. Again, we can think of the I part as a multiplier, equal to +1/2 or —1/2 depending on the spin state (a or f5) of each individual Ha nucleus. The observable magnetization is on Hb, and as it rotates around the axes (y —> — x -> —y —> x -> y) it alternates between in-phase and antiphase with respect to its coupling partner Ha. The effect of pulses is similar to what we saw for a pair, except that... 

To understand selective (shaped) pulses and the spin lock, we need to look in detail at the effect of pulses on spins as a function of their resonant frequency, v0, that is to say the position of a resonance within the spectral window. 

Ashauer R, Boxall ABA, Brown CD 2007a. Modeling combined effects of pulsed exposure to carbaryl and chlorpyrifos on Gammarus pulex. Environ Sci Technol 41 5535-5541. 

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