Noise can be controlled

Noise can be controlled in diode array spectrometry by spectral averaging. The Felgett advantage (noise reduction equals the square root of acquired data points) leads to a significant improvement of the signal-to-noise ratio. Large bandwidth acquisition not only reduces noise but also lowers sensitivity. 

Noise is controlled inside plants to provide a safe, healthful, and comfortable work environment. Noise is controlled outside plants to avoid degrading the neighborhood environment. Noise can be controlled directly at the source, such as a fan or transformer, where it is produced. Noise can also be controlled along the paths that it travels from the source to the receiver, for example, by the use of a barrier or a muffler. Noise can also be controlled at the receiver, for example, by earmuffs or earplugs, both of which were discussed earlier. This section addresses control of plant noise at the source and along propagation paths. 

The possible adverse effects of excessive noise exposure on hearing have been weU-estabhshed (Sliwinska-Kowalska et al., 2007, Nandi et al., 2008). To prevent occupational noise-induced hearing loss, collective measures can be taken to reduce the overall noise level at the work layout (Bies et al., 2003). Hearing protection is only used when these interventions are insufficient or unfeasible. Noise can be controlled by blocking the noise at the source, along its path from the source to the receiver, and at the end receiver (Hsu et al., 2004). 

Common controls. Noise can be controlled in the work environment by isolation or enclosure of the source of the noise. Control rooms can be constructed in treatment plants to provide a low-noise environment for operators. If operators must enter high-noise areas they can be required to use personal hearing protection to protect against high noise levels. 

Thunderous noise during an interruption, because of air blast. The intensity can be controlled by providing silencers... 

Frequently a modulation of light is introduced to the system in order to increase the signal to noise ratio. Flash lamps by their construction give pulses of light with repetition, which can be controlled by the user. Other lamps cannot be modulated through their driving current because the emitted radiation would be unstable over time. In this case, the application of an external modulator, e.g. a mechanical chopper, is the only solution. In both cases, the frequency of modulation is rather low - up to kilohertz. 

If there were no noise in the world, these factors would control the required sampling rate. However, because noise exists and noise can be aliased as well as data, the maximum noise frequency passed by the electronics system actually determines the required sampling rate. 

Expert systems are easy to program and to understand because they usually resemble instructions in English. The time and cost for developing these systems is relatively small. The primary problem usually turns out to be interpreting the sensors. Because first and second derivatives of sensor data are used to find trends and patterns, noise can be a major problem. The rules allow the controller to adapt to the condition of the material and to the geometry of the part. Expert systems make it relatively easy to change to backup plans when sensor or equipment failures occur. In fact, rule-based systems can be quite general and handle a number of materials with little material specific data. 

In the Andreev interferometers (see Fig. 1), the phase relations between the electron and hole wavefunctions in the normal wire can be controlled by the magnetic flux enclosed by a superconducting loop, which results in the periodic dependence of transport characteristics of the interferometer on the superconducting phase difference across the SNS junction. Initially, the oscillations of the conductance were investigated both experimentally (see a review in Ref. [11]) and theoretically [12], and, more recently, the oscillations in the current noise were reported [10]. 

When SRVs are called upon to operate, the valve discharge noise can be intense, reaching levels which may be considered harmful to operating personnel (see details later) or surrounding urban environments - that is, levels above those prescribed by most federal, state, environmental and local regulations. Unlike control valves, however, the noise of SRVs is not constant and should be of very limited duration, a consideration to be taken into account in the whole discussion around noise generated by SRVs. 

The effect of measurement noise can be observed for all variables (especially the control input, as shown in Fig. 5.5). In particular, the model-free observer based on RBFI is the most sensitive to measurement noise. 

The noise sources in control valves include mechanical vibration (usually below 100 dBA) hydrodynamic noise caused by liquid turbulence, cavitation, or flashing (usually below 110 dBA) and aerodynamic noise (can reach 150 dBA). In control valve design, aerodynamic noise can be a major problem. Aerodynamic noise generation, in general, is a function of mass flow rate and the pressure ratio (p /pf) across the valve. The point at which sonic speed is reached in the valve vena contracta is a function of the valve design. 

The basic concepts and seminal work in this field are from Taguchi, who stated that any product whose performance characteristics are different from the target values suffers a loss in quality, which he quantified by a parabolic function. He then classified factors as 1) control factors, which can be controlled under normal operating conditions and 2) noise factors, which are difficult, impossible, or very expensive to control. 

LQG-Benchmark The achievable performance of a linear system characterized by quadratic costs and Gaussian noise can be estimated by solving the linear quadratic Gaussian (LQG) problem. The solution can be plotted as a trade-off curve that displays the minimal achievable variance of the controlled variable versus the variance of the manipulated variable [115] which is used as a CPM benchmark. Operation close to optimal performance is indicated by an operating point near this trade-off curve. For multivariable control systems, H2 norms are plotted. The LQG objective function and the corresponding H2 norms are [115]... 

We assume that conditions can be controlled to minimize additional relaxation effects such as magnetic dipole-dipole interactions. As the number of relaxation mechanisms decreases, the information necessary for a line shape analysis of the spectra also decreases. Thus, a poorer signal-to-noise ratio can be tolerated, and the signal can be smoothed by curve fitting techniques. Since little is known at the molecular level about two-dimensional transport coefficients, such as the surface viscosity, large uncertainties can be tolerated. In this sense, we believe that much can be learned from monolayer experiments using spin label surfactants. 

Time-delayed feedback control has also been applied to purely noise-induced oscillations in a regime where the deterministic system rests in a steady state. It has been shown that in this way both the coherence and the mean frequency of the oscillations can be controlled in simple models [7-9, 49, 50] as well as in spatially extended systems [51-53]. 

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