Inventory buffer

Exploring the impact of parameters set by management Typically, management have to choose values for such parameters as inventory buffer capacities, the number of kanbans, or base stock levels. Queueing models enable their impact on performance measures such as throughput or service level to be found. If costs are available, then it is possible to determine the values that optimize performance. 

The system of just-in-time production, in which inventory buffers are kept to a minimum, does, in fact, increase the cost of aeddents to the firm. This logic does not apply to chronic health problems, however, and Wokutch documents the reluctance of Japanese firms to address the long-term consequences of its high-paced, high-stress production system - particularly cumulative trauma disorders. 

Safety stock costs If the demand time, the transit time, or both are uncertain, it may be necessary to carry inventory as a buffer against demand uncertainty. As discussed earlier, the extent of this inventory buffer depends on the magnitude of the demand uncertainty during the supply lead time and the planned in-stock service level. If the planned in-stock probability is expressed as service and the demand over lead time has a standard deviation of ct i, then the safety stock level is expressed as (Note that we assume that... 

Finished product Safety stock Inventory buffer for demand and supply volatility. 

Inventory buffers are placed in the first echelons closed to actual demand to cope with uncertainty... 

Capacity Planning and Inventory Management Supply capability Core competence Cycle time consistency Inventory, buffers Plexible response Lower variability Constraint elimination... 

Often more catastrophic failure in the supply chain because of the elimination of inventory buffers at each step in the supply chain... 

Determine proper inventory buffers (special levels) for routed parts leaving cell to back shops (i.e., welding, machining, plating, etc.). 

We referred in Chapter 9 to the potential of supply chain event management (SCEM) to enable better identification of the occurence of unplanned events (or the non-occurrence of planned events). Tools such as these can significantly reduce supply chain uncertainty and thus reduce the need for additional inventory buffers. Another emerging technology that is enabling dramatic improvements in visibility is Radio Frequency Identification (RFID). 

Process Conceptual Design Equipment selection and sizing Inventory of process Single vs. Multiple trains Utility requirements Overdesign and flexibility Recycles and buffer capacities Instrumentation and control Location of plant Preliminary plant layout Materials of construction As above plus equipment suppliers data, raw materials data, company design procedures and requirements... 

Storage. Some of the largest inventories of hazardous materials tend to be held up in the storage of raw materials and products and intermediate (buffer) storage. 

Many rate constants in aqueous solutions are pH or pD sensitive. In particular, enzyme catalyzed reactions often show maxima in plots of pH(pD) vs. rate. The example in Fig. 11.5 is constructed for a reaction with a true isotope effect, kH/kD = 2, and with maxima in the pH(pD)/rate dependences as shown by the bell shaped curves. These behaviors are typical for enzyme catalyzed reactions. When the isotope effect is obtained (incorrectly) by comparing rates at equal pH and pD, the values plotted along the steep dashed curve result. If, however, the rate constants at corresponding pH and pD (pD = pH + 0.5) are employed, a constant and correct value is obtained, kH/kD = 2. Thus for accurate measurements of the isotope effects one must control pH and pD at appropriate values (pD = pH + 0.5 in our example) using a series of buffers. In proton inventory experiments (see below) buffers should be employed to insure equivalent acidities across the entire range of solvent isotope concentration (0 < xD < 1), xD is the atom fraction of deuterium [D]/([H] + [D]). 

In both the baseline incineration system and the modified baseline process, energetics are removed in explosive containment rooms (ECRs) as part of the agent destruction operation in the munitions demilitarization building (MDB). A work-in-progress (WIP) buffer inventory is provided between the energetics removal step and the rest of the operation. The same type of energetics removal equipment is used in both the baseline system and the modified baseline process. 

Unlike the baseline system, which uses a LIC to destroy most of the agent, in the modified baseline process, all agent is destroyed in the MPF and its afterburner. Consequently, the MPF is the critical element in the modified baseline process. Sufficient machinery for accessing agent and sufficient WIP buffer inventory will be necessary to ensure that facility throughput is determined by the capacity of the MPF and that the MPF is not starved for input feed materials. 

It is equally important to avoid psychological safety buffers in all steps of the supply chain. Since the preceding step is not next door any more in a global supply chain setup (e.g., between the raw materials supplier and the manufacturer of the finished goods), processes are a black box and people tend to err on the safe side, driving inventories up. 

In general, there are three types of stock to consider. Cycle stock is the regular inventory that is needed to fulfill orders. Buffer, or safety, stock is additional inventory that is needed in case of a supply or demand fluctuation. Anticipatory, or speculative, stock is inventory that is kept on hand because of expected future demand or expected price increase (e.g., flu vaccine in the fall and winter months). Buying anticipatory stock is risky, and therefore, pharmacists usually do not carry much anticipatory stock and place higher markups on such anticipatory stock. These types of stock are important to consider when deciding how much to order and when to order (Silbiger, 1999). 

Discrimination among all of these is a trivial exercise. Both B vitamins and C were easily quantitated in prepared mixtures as expected [59], but it was also relatively easy to measure each one after its simple extraction into aqueous buffer from pharmaceutical preparations, as well as (in the case of vitamin C) from extracts of fruit, fruit juices, and vegetables. A very thorough inventory of tests for possible interferences was run and the resultant analytical data for the vitamins compared extremely well with the labelled contents on the packages of pharmaceutical products and with the data in compendia that list the average compositions of vitamins and other essential products in plant food materials [33]. Analysis of the major fat soluble D2 and D3 vitamins (ergocalciferol and cholecalciferol) has not progressed with the... 

The control structure discussed in this section is presented in Figure 4.4(a). The reactor-inlet flow rate is fixed at the value l. Reactor effluent controls the reactor holdup V, while the coolant flow rate controls the reactor temperature. Dual composition control is used for the distillation column. The reactant is fed on level control. For illustration purposes, a buffer vessel was considered. This increases the equipment cost and might be unacceptable due to safety or environmental concerns. An alternative is to feed the reactant in the condenser dram of the distillation column. This strategy achieves the regulation of reactant inventory, because any imbalance is reflected by a change of the holdup. 

Figure 2 shows the Current simulation model. This figure illustrates that buffers (inventories) are located before and after each test station and operation products are transported between all operations and test stations. 

A distillation unit has been designed to handle a very hazardous material. The unit utilizes a reflux drum and buffer storage. List several ways in which the inventory of the hazardous material can be reduced or eliminated. Sketch and instrument the system that is recommended. 

The molecular components of many buffers are too large to reach the active site of carbonic anhydrase. Carbonic anhydrase II has evolved a proton shuttle to allow buffer components to participate in the reaction from solution. The primary component of this shuttle is histidine 64. This residue transfers protons from the zinc-bound water molecule to the protein surface and then to the buffer (Figure 9.30). Thus, catalytic function has been enhanced through the evolution of an apparatus for controlling proton transfer from and to the active site. Because protons participate in many biochemical reactions, the manipulation of the proton inventory within active sites is crucial to the function of many enzymes and explains the prominence of acid-base catalysis. 

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