Frequency bandwidth

Single mode generation can be achieved by carefully controlling the frequency and wavenumber bandwidths of the excitation. The frequency bandwidth can readily be limited by employing windowed toneburst excitation signals [2] while the wavenumber bandwidth is... 

The foremost of the modem teclmiques is tlie use of lasers as spectroscopic tools. Lasers are extremely versatile light sources. They can be designed with many usetlil properties (not all in the same instmment) such as high intensity, narrow frequency bandwidth with high-frequency stability, tunability over reasonable frequency ranges, low-divergence beams which can be focused into very small spots, or pulsed beams with... 

Most molecular vibrations are well described as hannonic oscillators with small anlrannonic perturbations [5]. Por an hannonic oscillator, all single-quantum transitions have the same frequency, and the intensity of single-quantum transitions increases linearly with quantum number v. Por the usual anhannonic oscillator, the single-quantum transition frequency decreases as v increases. Ultrashort pulses have a non-negligible frequency bandwidth. Por a 1... 

The frequency bandwidth, in Hz, of a weak, selective pulse is approximately given by Av— 1/Tp, where Tp is the pulse duration in ms. 

Nonselective pulse A pulse with wide frequency bandwidth that excites all nuclei of a particular type indiscriminately. 

Noise is characterized by the time dependence of noise amplitude A. The measured value of A (the instantaneous value of potential or current) depends to some extent on the time resolution of the measuring device (its frequency bandwidth A/). Since noise always is a signal of alternating sign, its intensity is characterized in terms of the mean square of amplitude, A, over the frequency range A/, and is called (somewhat unfortunately) noise power. The Fourier transform of the experimental time dependence of noise intensity leads to the frequency dependence of noise intensity. In the literature these curves became known as PSD (power spectral density) plots. 

The large increase of the high-frequency bandwidth is but one challenge for the nuclear dynamics theories of hydrogen bonding, which are the subject of this chapter. Other challenges are the band asymmetry, the puzzling appearance... 

The signal supplied by cryogenic sensors is very low (in the order of jlV). The white noise voltage is proportional to the frequency bandwidth. To reduce the bandwidth, low-pass filters (carachteristographers with 0.01 Hz cut-off) or band-pass filters (lock-in) are used. The former method is more precise, but a longer time for the measurements is required. 

When the light is dominated by massive stars, e.g. in starburst galaxies, the luminosity is related in turn to the rate of metal production, since virtually all processed material is ejected in the form of metals (and some helium). Thus there is a relationship between the total co-moving luminosity density, the monochromatic luminosity density (deduced from star-forming galaxy redshift surveys with appropriate corrections for absorption) in a fixed frequency bandwidth (anywhere between 912 and about 2000 A in the rest frame) and the mass going into nucleosynthesis ... 

Frequency domain techniques offer advantages over time domain techniques for real-time applications. In the frequency domain the measurements are performed within limited frequency bandwidths. The noise in limited bandwidths is reduced, in most cases substantially. Figures 9.7 illustrates this concept. In Figure 9.7a the... 

Figure 9.7. Noise content of a fiberoptic oxygen sensor signal (a) in the time and (b) in the frequency domains. Time domain signals require broad frequency bandwidths. Frequency domain signals require very limited-frequency bandwidths. Noise is reduced by band limiting the signal, an advantage of frequency domain methods.

Bartlett and Corle [46] proposed modification of Maxwell s equations in the vacuum by assigning a small nonzero electric condictivity to the formalism. As pointed out by Harmuth [47], there was never a satisfactory concept of propagation velocity of signals within the framework of Maxwell s theory. Thus, the equations of the latter fail for waves with nonnegligible relative frequency bandwidth when propagating in a dissipative medium. To resolve this problem, a nonzero electric conductivity ct and a corresponding current density... 

A new class of lasers, so called vibrionic solid state lasers, can emit—in contrast to mher solid slate lasers—a comparatively broad range of wavelengths. The lower level in these lasers is a band of energy levels that is caused by interaction between the electron motion and lattice vibrations. With ihe help of Ihe usual tools (filters, ctalons etc.) a narrow and tunable frequency bandwidth is selected for the laser output. The most popular materials arc Ti-sapphire. i.e.. titanium doped Al-Oi with output range from hOO to 118(1 nm and Alexandria. i.e.. chromium doped BeAFOi lasing between about 700 and 825 nm. 

At the end of this section some useful interrelations are established between the free parameters of the model and the features of the calculated spectra, such as the absorption-peak frequency, bandwidth, and position of the low-frequency loss maximum. 

The signal of interest has been calculated above. Now, the noise needs to be estimated. Noise is defined as all the signal sources that are not of interest, but superpose the signal of interest. In our case the thermal noise and related sources, which is system immanent to any circuit is almost negligible even for small sample sizes, as the following calculation will show. The thermal noise of a 10 kfl resistor R at room temperature with a frequency bandwidth A/ of 100 kHz can be calculated to... 

Tables of Parameters based on the constant frequency bandwidth assumption...

The study that we describe below was inspired by our work on fitting the dynamic susceptibilities measurements for real assemblies of fine particles. Those data typically describe polydisperse systems in the low-frequency bandwidth a>/2% = 1 — 103 Hz. As To 10 s or smaller, then, using formula (4.132) for estimations, one concludes that the frequency interval mentioned becomes a dispersion range for the interwell (superparamagnetic) mode at coto< ct > 1, that is, a > 10. For temperatures up to 300 K, this condition holds for quite a number of nanomagnetic systems. 

Piezoelectric filter A kind of electromechanical device in which electrical signals are converted to a mechanical wave by using a piezoelectric crystal. Thus, the former electric wave is delayed as it propagates across the crystal, and this delay is used to reinforce a desired frequency bandwidth with very high Q values. The quartz crystal is an example of the piezoelectric elements used for these filters [i],... 

More detailed information can be obtained from noise data analyzed in the frequency domain. Both -> Fourier transformation (FFT) and the Maximum Entropy Method (MEM) have been used to obtain the power spectral density (PSD) of the current and potential noise data [iv]. An advantage of the MEM is that it gives smooth curves, rather than the noisy spectra obtained with the Fourier transform. Taking the square root of the ratio of the PSD of the potential noise to that of the current noise generates the noise impedance spectrum, ZN(f), equivalent to the impedance spectrum obtained by conventional - electrochemical impedance spectroscopy (EIS) for the same frequency bandwidth. The noise impedance can be interpreted using methods common to EIS. A critical comparison of the FFT and MEM methods has been published [iv]. 

Frequency range 34.5-35.5 Mcps 26.5-27.5 Mcps Number of channels 21 Bandwidth/6dB approx. 14kcps Low frequency output 6dBm/600 ohms Low frequency bandwidth 0.3-3.4 kcps Type of protection EEx ia I Certificate BVS 92.C.1208 U... 

The use of magnetic field modulation together with phase-sensitive detection using a lock-in amplifier renders CW-NMRI an extremely narrow-bandwidth detection technique, and thus the penalty inherent in all other techniques of a reduced SNR with increasing gradient strength (due to the increased frequency bandwidth) is removed. 

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