Closed for Changes

There are four fundamental and yet important software design principles—low coupling, high cohesion, open for extension, and closed for changes. We can simply call them high-low open-closed principles. 

Open (for Extension) - Closed (for Changes) Principles Modules should be open for extension and adaptation and closed for modification in ways that affect its clients. 

Figure 2.5 A design that is open for extension and closed for changes.

The implementation of the ChemDBQueryBuilder interface is determined at runtime depending on which implementation is passed into the CompoundMapper s constructor. This design makes the CompoundMapper open for extension while remaining closed for changes. Switching to a different vendor database does not require changes in CompoundMapper. All it requires is an implementation of ChemDBQueryBuilder for that vendor, which is passed into CompoundMapper s constructor so the CompoundMapper object knows which one to use at runtime. 

Drug interactions with this new classification of atypical medications are multiple. Therefore, it is essential to take a thorough medication history. Clozapine (Clozaril), risperidone (Risperdal), sertindole (Serlect), olanzapine (Zyprexa), and quentiapine (Seroquel) are fairly new and a long history of use in the practice setting has not been established. There are many side effects and possible interactions that have not been discovered yet. It is imperative that potential drug interactions be recorded and monitored closely for changes in efficacy, toxicity, and if applicable, drug concentration (Lam, 2000). 

When possible, quantitative analyses are best conducted using external standards. Emission intensity, however, is affected significantly by many parameters, including the temperature of the excitation source and the efficiency of atomization. An increase in temperature of 10 K, for example, results in a 4% change in the fraction of Na atoms present in the 3p excited state. The method of internal standards can be used when variations in source parameters are difficult to control. In this case an internal standard is selected that has an emission line close to that of the analyte to compensate for changes in the temperature of the excitation source. In addition, the internal standard should be subject to the same chemical interferences to compensate for changes in atomization efficiency. To accurately compensate for these errors, the analyte and internal standard emission lines must be monitored simultaneously. The method of standard additions also can be used. 

The oxygen sensor closed loop system automatically compensates for changes in fuel content or air density. For instance, the stoichiometric air/fuel mixture is maintained even when the vehicle climbs from sea level to high altitudes where the air density is lower. 

NTU (Number of Transfer Units) The NTU required for a given separation is closely related to the number of theoretical stages or plates required to cariy out the same separation in a stagewise or plate-type apparatus. For equimolal counterdiffusion, such as in a binary distillatiou, the number of overall gas-phase transfer units Nqg required for changing the composition of the vapor stream from yi to yo is... 

A similar effect was observed for changes in hood flow rate. With a fixed cross-draft velocity, capture efficiency decreased with decreasing hood flow rate. This effect was much more important when freeboard height was small. Their results showed that when hood flow rate was 1.5 m s m, efficiency remained close to 1.0 as long as the cross-draft velocin. was less than 0.45 in s. The most severe conditions tested were a hood flow rate equal to 0.33 m s" nr- and crossdraft velocity equal to 1.15 m s. Under these conditions, capture efficiency was equal to 0.83 for freeboard hei t equal to 0.3 m, but decreasing to 0.4 when freeboard height was decreased to 0.1 m. 

These relations do not hold closely for large impeller cuts, as the head and capacity drop a litde faster than the relations indicate. Allowance should be made by a trial-and-error approach when actually reducing an impeller size. Efficiency will remain nearly constant during all of the changes discussed. 

The study will commence with the administration of low doses, as judged from the non-clinical data. As the study progresses - and provided that there are no indications that it is unsafe to do so - the dosage levels may be increased past the anticipated therapeutic range. Subjects are closely monitored for changes in vital signs (blood pressure, heart rate, body temperature, etc.) and the emergence of any adverse side effects (nausea, drowsiness, pain, headache, irritability, hair loss, etc.). 

Pediatric patients should be observed closely for suicidality, worsened depression, agitation, irritability, and unusual changes in behavior, especially during the initial few months of therapy or at times of dosage changes. Furthermore, families and caregivers should be advised to monitor patients for such symptoms. 

Snap-in tabs, above each end of the output meter, indicate the direction the final control element moves for a change in the output signal. Tabs normally read "open-close" for control valves and "slow-fast" for variable-speed motors, or other appropriate designations. 

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