Pressure response characteristics

Roller presses that are used for the compaction offertilizers (Fig. 6.6-16) feature selfaligning roller bearings, optimally sized steel bearing blocks, and a hydraulic pressurizing system with proprietary functions and hydraulic accumulators. The latter allow adjustment of the pressure-response characteristic and provide for overload protection. While in some cases simple gravity feeders with flow control baffles are provided, most applications require one or more screw feeder(s) with variable (e.g., hydraulic) speed drives to force the material to be compacted into the nip between the rollers [B.48, B.97]. 

The best anti-surge control is the simplest and most basic that will do the job. The most obvious parameter is minimum-flow measurement, or if there is a relatively steep pressure-flow characteristic, the differentia pressure may be used. The latter parameter allows for a much faster response system, as flow measurement response is generally slow however, the speed of response need only be fast enough to accept expected transients. One major problem with the conventional methods of measurement and control is the need to move the set point for initiation of the control signal away from the exact surge point to allow some safety factor for control response time and other parameters not directly included... 

If the reactor has a relief device, the pressure response depends on the relief device characteristics and the properties of the fluid discharged through the relief. This is illustrated by curve A (Figure 8-2) for vapor relief only and by curve B for a two-phase froth (vapor and liquid). The pressure will increase inside the reactor until the relief device activates at the pressure indicated. 

Some pharmacokinetic characteristics and the initial and usual maintenance dosages of hydrochlorothiazide are listed in Table 11-2. Although thiazide diuretics are more natriuretic at higher doses (up to 100-200 mg of hydrochlorothiazide), when used as a single agent, lower doses (25-50 mg) exert as much antihypertensive effect as do higher doses. In contrast to thiazides, the blood pressure response to loop diuretics continues to increase at doses many times greater than the usual therapeutic dose. 

In turbulent flows, even when the mean flow is steady (see below), the flow variables, i.e-., velocity, pressure, and temperature, all fluctuate randomly with time due to the superposition of the turbulent eddies on the mean flow. For example, if the temperature at some point in the flow is measured by means of some device which has very good time response characteristics and the output of this device is displayed on a suitable instrument then a signal resembling that shown in Fig. 2.10 will be obtained in turbulent flow. 

As discussed above, agents acting via o -ARs to elicit changes in blood pressure induce a characteristic biphasic hemodynamic profile consisting of a transient hypertensive response followed by the sustained, centrally localized o -AR-mediated drop in blood pressure. As with the a2A-AR, mice null for the o ij-AR (a2B-AR / ) have documented the role of the a2B-AR subtype in modulating the pressor, or increased, blood pressure responses following a2-agonist activation of peripheral mechanisms (11). Control studies demonstrated that a2B-... 

Ganglion blockers prevent ANS reflexes, including changes in heart rate elicited by increases or decreases in mean blood pressure. This characteristic can be of value in questions of drug identification because it helps to determine if a drug action (e.g., on heart rate) is direct or due to an autonomic reflex response. For the USMLE, this is the main relevance of ganglionic blockers. 

Pressure is commonly controlled in systems using diaphragm or piston pumps by adjusting the proportion of the output flow from the pump that is diverted into a return line back to tank. This can be actuated by a simple butterfly valve, an adjustable spring-loaded ball valve, or a valve based on the use of air pressure to control the line pressure. Measurements of the response characteristics of commercially available valve systems have shown that most are able to achieve within 10% of a set value in less than 10 s (Rietz el a/., 1997), and this then has formed the basis of environmental performance standards for agricultural crop sprayers that have recently been agreed within the European Community. 

Fig. 6. Sinusoidal forcing of volume with pressure response. A measure of volume and pressure as f(t)i The values of B, the pressure amplitude, and tj), the phase shift, will be constant for a given value of volume amplitude, A, and for a given value of angular frequency, tOi. Both B and (j> will, in general, vary as cu is changed, as they are a function of the system adsorption characteristics. The angular frequency, o), is varied by changing the time required to complete the one cycle (the period).

Demonstrate rapid reformer start-up based on low pressure-drop concepts. This reactor design should also provide improved transient response characteristics. 

In the frequency response method, first applied to the study of zeolitic diffusion by Yasuda [29] and further developed by Rees and coworkers [2,30-33], the volume of a system containing a widely dispersed sample of adsorbent, under a known pressure of sorbate, is subjected to a periodic (usually sinusoidal) perturbation. If there is no mass transfer or if mass transfer is infinitely rapid so that gas-solid mass-transfer equilibrium is always maintained, the pressure in the system should follow the volume perturbation with no phase difference. The effect of a finite resistance to mass transfer is to cause a phase shift so that the pressure response lags behind the volume perturbation. Measuring the in-phase and out-of-phase responses over a range of frequencies yields the characteristic frequency response spectrum, which may be matched to the spectrum derived from the theoretical model in order to determine the time constant of the mass-transfer process. As with other methods the response may be influenced by heat-transfer resistance, so to obtain reliable results, it is essential to carry out sufficient experimental checks to eliminate such effects or to allow for them in the theoretical model. The form of the frequency response spectrum depends on the nature of the dominant mass-transfer resistance and can therefore be helpful in distinguishing between diffusion-controlled and surface-resistance-controlled processes. 

Wang, M., Evans, J., and Knapp, C. 1995. Spectral patterns and frequency response characteristics of arterial pressure in heart paced dogs. IEEE Trans. Biomed. Eng. 42 708-717. 

Soil stress-strain characteristics and pore pressure response under cyclic loading... 

All of these pressure transducers offer frequency response characteristics acceptable for most or all respiratory applications. In situations requiring the measurement of a single pressure (for example, the pressure at the mouth during breathing), one of the two input ports to the transducer is left open to atmospheric pressure. In other situations requiring the measurement of a pressure differential (for example, measuring the output of a pressure-drop flow sensor), the two ports of the transducer are attached to the two taps of the sensor. 

Ernst ME, Carter BL, Zheng S, Grimm RH Jr. Meta-analysis of dose-response characteristics of hydrochlorothiazide and chlorthalidone effects on systolic blood pressure and potassium. Am J Hypertens 2010 23(4) 440-6. 

This very simple model having the adsorbed layer formed on the surfaces of the electrode and the electrolyte has allowed us to successfully interpret the response time of oxygen sensors systematically measured under various conditions and the deviations from ideal behavior due to the oxygen semipermeability flux [10,11]. The existence of the adsorbed layer becomes the most important factor to determine the response characteristics of the device to the oxygen pressure. 

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