Attrition rates

Virtual screening allows the scope of screening to be extended to external databases. When this is done, increasingly diverse hits can be identified. The application of virtual. screening techniques before or in parallel with HTS hclp.s to reduce the assay-to-lcad attrition rate observed from HTS. In addition, virtual screening is faster and less expensive than experimental synthesis and biological testing. 

For group B and D particles, nearly all the excess gas velocity (U — U,nj) flows as bubbles tnrough the bed. The flow of bubbles controls particle mixing, attrition, and elutriation. Therefore, ehitriation and attrition rates are proportional to excess gas velocity. Readers should refer to Sec. 17 for important information and correlations on Gel-dart s powder classification, minimum fluidization velocity, bubble growth and bed expansion, and elutriation. 

Variances in resin performance and capacities can be expected from normal annual attrition rates of ion-exchange resins. Typical attrition losses that can be expected include (1) Strong cation resin 3 percent per year for three years or 1,000,000 gals/ cu.ft (2) Strong anion resin 25 percent per year for two years or 1,000,000 gals/ cu.ft (3) Weak cation/anion 10 percent per year for two years or 750,000 gals/ cu. ft. A steady falloff of resin-exchange capacity is a matter of concern to the operator and is due to several conditions ... 

If it is assumed that the impaet erystal-impeller attrition rate is a funetion of ... 

Then the crystal-impeller impaet attrition rate may be deseribed by Synowiee etal. (1993)... 

Then the crystal-crystal attrition rate may be expressed as... 

Whenee the fluid turbulence attrition rate is given by... 

The respeetive dependeneies of attrition rate on partiele number, n, and size, Lq, and average unit power input, e, for eaeh meehanism eonsidered are summarized in Table 5.1. 

A signifieant effeet of impeller hardness on the average attrition rate was also deteeted supporting the observations of Evans etal. (1974) and Shah etal. 

The maximum contribution of turbulent attrition rate varies in the range 30-40 per cent of total fine numbers with the assumption that impact attrition fragments are not generated by the rubber coated turbine (i.e. similar to the 25 per cent estimate of Evans etal., 1974). 

In the analysis of Synowiee etal. (1993), while the turbulent attrition rate is predieted to be eonstant with inereasing seale of operation at eonstant power input, the impaet attrition rate is predieted to deeline with the square of vessel size. In eombination... 

Figure 5.17 Effect of scale-up factor (

The concentration of the ZSM-5 additive should be greater than 1% of the catalyst inventory to see a noticeable increase in the octane. An octane boost of one research octane number (RON) will typically require a 2% to 5% ZSM-5 additive in the inventory. It should be noted that the proper way of quoting percentage should be by ZSM-5 concentration rather than the total additive because the activity and attrition rate can vary from one supplier to another. There are new generations of ZSM-5 additives that have nearly twice the activity of the earlier additives. 

The improvements in the catalyst s binder properties will reduce the catalyst attrition rate thus, lowering the flue gas stack opacit This improvement allows refiners to use a harder catalyst without adversely affecting the catalyst s fluidization properties. 

LEs are very intuitive and therefore easy to apply. For the simplest case of directed fire, for example, they embody the idea that one side s attrition rate is proportional to the opposing side s size. However, LEs are applicable only under a... 

Most traditional models focus on looking for equilibrium solutions among some set of (pre-defined) aggregate variables. The LEs are effectively mean-field equations, in which certain variables (i.e. attrition rate) are assumed to represent an entire force, the equilibrium state is explicitly solved for and declared the battle outcome. In contrast, ABMs focus on understanding the kinds of emergent patterns that might arise while the overall system is out of (or far from) equilibrium. 

Characteristics of attrition and adsorption were investigated to remove CO2 in fluidized hed using activated carhon, activated alumina, molecular sieve 5 A and molecular sieve 13X. For every dry sorbent, attrition mainly still occurs in the early stage of fluidization and attrition indexs(AI) of molecular sieve 5A and molecular sieve 13X were higher than those of activated carbon and activated alumina. Percentage loss of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but that of activated carbon and activated alumina were 8.3% and 8.1%, respectively. Overall attrition rate constant (Ka) of activated alumina and activated carbon were lower than other sorbents. 

Gas velocity is an important operating condition in the fluidized bed process and it can highly affect the attrition of dry sorbents. Therefore, the weight remaining in the bed with fluidization time for gas velocity of 20.59 cm/s, 25.74 cm/s, and 30.89 cm/s was measured to estimate the attrition of dry sorbent with gas velocity. As shown in Fig. 4, attrition mainly occurred in the early stage of fluidization. The attrition rate with time decreased and the regression equations fit natural log functions. In addition, Fig. 4 shows that the attrition of dry sorbents is highly affected by gas velocity in the fluidized bed process. 

Table 2 summaries overall attrition rate constants (Ka) and physical properties for each dry sorbent. As shown in Table 2, Ka of activated alumina was the lower than any other sorbent, but was similar to activated carbon. However, we used activated carbon as dry sorbent to control CO2 because it is the most cost-effective among others.

Table 2. Summary of attrition rate constants for dry sorbents at gas velocity of 20.59 cm/s...

Kola, I., Landis, J. Can the pharmaceutical industry reduce attrition rates Nat. Rev. Drug Discov. 2004, 3, 711-716. 

A small, flexible dose study of citalopram (dosage range = 10-40 mg/day) in 14 Hispanic and 6 non-Hispanic (non-White) depressed HIV-positive patients conducted in Miami also showed no differences in response rate or effective dose between ethnicities (Currier etal., 2004). In addition, Hispanic patients did not have a significantly higher attrition rate compared to non-Hispanics. 

As ADME/PK has become incorporated into drug discovery it has become necessary to reconsider the purpose of the studies. If the science is really going to reduce the attrition rate in development, then it is essential for the studies to allow predictions of the PK in man to be made. This means predicting the likely size and frequency of the dose. A review of the top 10 medicines of 1999 (Table 6.1) shows all of them to be once-a-day compounds. It is clear that to be best in class , and to be able to maintain that position as follow-up compounds come along, it seems probable that a compound will need to be suitable for once a day dosing. 

There can also be substantial particle attrition in cyclones in fluidized-bed systems because particles are accelerated at the inlet of the cyclone and impacted against the cyclone wall. Although there is little information on particle attrition in cyclones in the literature, it has been reported (Sishtla) that increasing system pressure decreases the attrition rate in cyclones operating with coal char. The mechanism by which this occurred was not determined. 

The attrition rate, i.e., the rate of generation of fines, 0-d microns, at the submerged jets in a fluidized bed, tends to fall off asymptotically with time to a steady-state rate as shown in Fig. 9. Initially the attrition rate is high due to the wearing off of angular comers. Typically, it takes long time, hours to days, for the particles to reach steady-state (equilibrium) where the particles tend to be more rounded. For most catalytic fluidized bed processes, the bed operates at equilibrium. That means the most significant part of the attrition rate curve is the steady-state rate. 

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