Modified filters

Plate pr esses. Sometimes called sheet filters, these are assemblies of plates, sheets of filter media, and sometimes screens or frames. Thev are essentially modified filter presses with practically no cakeholding capacity. A press may consist of many plates or of a single filter sheet between two plates, the plates may be rectangular or circular, and the sheets may lie in a horizontal or vertical plane. The operation is similar to that of a filter press, and the flow rates are about the same as for disk filters. The operating pressure usually does not exceed 138 kPa (20 psig). The presses are used most frequently for low-viscosity liqmds, but an ordinaiy filter press with thin frames is commonly used as a clarifier for 100-Pa s (1000-P) rayon-spinning solution. Here the filtration pressure may be 6900 kPa (1000 psig). 

Noise is a serious problem where z(co) is small. We see that the estimate 6(cd) carries with it none of the sensible noise treatment that modified filters like those of the Wiener type provide. We may, however, supply the required noise suppression between iterations by smoothing. The polynomial filters described in Section III.C.5, for example, may be used. Very little has been done, however, to determine how suppression might be accomplished optimally. Usually it is treated in an ad hoc way. 

Modified filter sampling methods that are available will measure ambient levels of strong acid in ambient aerosol samples, and these methods do so with acceptable precision and accuracy [as indicated by the balance between measured anions and cations (56, 57)] in the absence of significant levels of particulate weak acids. Additional intercomparisons involving intrinsically different techniques for particulate strong acidity [e.g., IR spectroscopy (48), thermal speciation (38, 45), and filter methods (28)] are needed. Further information on the occurrence of various weak acids in airborne particles is needed, along with further studies of techniques for their specific determination in atmospheric aerosol samples. 

The phase vocoder has been useful in a number of applications4. In time-scale modification, for example, the goal is to maintain the perceptual quality of the original signal while changing its apparent rate of articulation . In performing time-scale modification with the phase vocoder, the instantaneous frequency and amplitude of each channel are interpolated or decimated to a new time scale . In one scenario, the phase of each filter output in Equation (9.9) is first unwrapped, and the channel amplitude and unwrapped phase are then time scaled. With time-scale modification by a factor p, the modified filter output is given by... 

Finally, based on the channel assignment a phase correction is introduced in each channel, making the phase of the modified filter output yp (n) at time n = pnpQ equal to the phase at the time instant n = np in the original time scale. Denoting the phase correction for each cluster by <]), the modified channel signal becomes... 

Ultrafiltration Sols pass through an ordinary filter paper. Its pores are too large to retain the colloidal particles. However, if the filter paper is impregnated with collodion and then dipped in HCHO or glacial acetic acid, the pore size is much reduced. Such a modified filter paper is called an ultra-filter. ... 

The two-dimensional distribution of nickel throughout the modified filter disc was examined with SEM/DEX (energy dispersive X-ray) on a polished radial cross section of the disc. The analysis was performed on a JSM 6400 (JEOL) equipped with a NORAN X-ray analysis system. The K line of nickel was used as the X-ray analysis line. The electron probe worked at an acceleration voltage of 15-25 kV and a current intensity of 3 x lO A. 

Fig. 3. SEM/DEX mapping for Ni of a cross section of a nickel-modified filter disc after a single deposition cycle with the urea method.

Fig. 5 shows the benzene conversion as a function of the reaction temperature and gas velocity with a 1 wt % nickel-modified filter disc. As a reference, the benzene conversions using a blank disc (no catalyst inside) in the same conditions are displayed in the figure. It was found that full conversion of benzene was obtained at typical filtration gas velocities (2.5 and 4 cm/s) and in a temperature range from 750°C to 900°C. Even at a higher filtration velocity such as 6 cm/s, a complete conversion is still reached above 800 °C. 

Fig. 6 shows the naphthalene conversion as a function of the reaction temperature and gas velocity with a 1 wt % nickel-modified filter disc. The blank disc was also used as a reference. As shown in Fig. 6, almost complete naphthalene cracking was achieved above 800 °C with any gas velocity lower than 4 cm/s. Even with a gas velocity of 6 cm/s, the conversion still remains about 97 %. However, below 800 °C the conversion of naphthalene significantly decreased as the reaction temperature decreased and the gas velocity increased. In addition, benzene was identified as one reaction product of naphthalene cracking at 750 and 800 °C. Table 1 lists the amount of benzene in the outlet gas after reaction over the nickel-modified filter disc. It is evident that for all gas velocities at 750 °C, benzene is present in the outlet gas with a significant amount. Above 800 °C,... 

In a modified version of the pharmacophore point filter, a score equal to 1 is allowed to qualify a compound as drug-like if the pharmacophore point present in the compound is of type carboxylic acid, amine, guanidine, or amidine. This modified filter was defined to correctly classify the small active drugs belonging to the central nervous system (CNS) class. 

Solar simulators usually consist of a light source and spectral output modifying filters. The light intensity at the exposure plane (irradiance) may be adjusted through lamp power, the source to specimen distance, attenuating filters or a combination of these. 

Figure 10.4 FE-SEM images of (a) the native cotton fiber, (b) the modified cotton fiber, and (c) the modified cotton fabric at low magnification, (d) A three-dimensional AFM image of the modified fiber surface, (e) an image of water droplets on the surface of the modified colored cotton fabric, and (f) an image of water droplets on the surface of the modified filter paper [11].

Membrane filter presses are modified filter presses with the introduction of inflatable membrane systems. 

This thermally induced phase separation immunoassay has been extended by grafting PNIPAM to porous nylon membranes on microfiuidic cards. At temperatures above the LCST of PNIPAM, the polymer-antibody conjugates are aggregated and retained on the modified filters, while other proteins can pass through. Below that temperature, the captured and labelled antigens are released as a concentrated pulse (Golden et al, 2010 Nash era/., 2010). 

Bruil A, Oosterom HA, Steneker I et al. Poly(ethyleneimine) modified filters for the removal of leukocytes from blood. J Biomed Mater Res 1993 27 1253-1268. 

Hou K, Gerba CP, Goyal SM et al. Capture of latex beads, bacteria, endotoxin and viruses by charge modified filters. Appl Environ Microbiol 1980 40 892-896. 

The convolution kernel hix ) in Eq. (6) is an inverse Fourier transform of co, but its exact form is not realizable in practice. Therefore, several modified filter functions have been suggested. The selection of a particular filter function will affect the characteristics of the reconstructed image, that is, the desired image resolution and contrast. 

Delval, R, Crini, G., Vebrel, J., Knorr, M., Sauvin, G., Conte, E. Starch-modified filters used for the removal of dyes from waste water. Macromol Symp. 2003, 203, 165-671. 

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