The Year 2000 Problem
Computers' Year-2000 problem (Y2K), whereby some computer software won't recognize any digits as representing years in the 21st century, may well strike hoteliers particularly hard due to hotels' reliance on date-sensitive data (room reservations, for example). Moreover, unless hotels' software is updated, Y2K will manifest itself sooner among hotels than in many other industries, as hotels begin to book rooms in the year 2000. Hoteliers can (1) choose to do nothing (i.e., wait and see what actually happens), (2) debug their existing computer applications, or (3) purchase and install all new systems software. Some methods to remove the Y2K problem include these five techniques: size expansion, data encoding, date shift, soft windows, and hard windows. Replacing existing application software with new, Y2K-compliant computer software will resolve the problem. That approach, however, means that all of a hotel's related computer-program requirements be accounted for—which is an enormous undertaking. Moreover, new computer systems are costly, and “off the shelf” business software rarely is of much help to hoteliers. As a result, hotels' computer systems and software most often require extensive customization. Time is short; hoteliers don't have until 2000 to solve their Y2K problems, since a hotel's existing reservation system may not be able to recognize reservations for the year 2000 (“00”). In practical terms, the time required for software development and testing is substantial. Therefore, hotels need to handle the Y2K issue immediately.
The year 2000
Consequently, 2000 gets an extra day because it is divisible by 4. It does not because it is divisible by 100. But 2000 is divisible by 400. Therefore, from Mar. 1, 1900 until Feb. 28, 2100, for 200 years, we have an unbroken pattern of an extra day every four years, without exception—thanks to the year 2000. This makes it simple to calculate a calendar within that special period—just add an extra day every four years, with no further complications. As an example, a very expensive Swiss watch advertises its 200-year calendar within precisely that period, and for good reasons. They can simply represent the year in binary form; 2000 in binary form is 1 1 1 1 1 0 1 0 0 0 0, and check that the last two digits are 0. In that year, add an extra day to the month of February. Their chip doesn’t even have to do any arithmetic for this. Why then has the “Year 2000” started to sound apocalyptic? It has everything to do with two habits inherited from a typewriter keyboard devised some 100 years ago and paper punch cards of 50 years ago. Let me first say that to many of us who have been using APL (A Programming Language), available for nearly 30 years, 2000 is a nonproblem. We have kept track of combined dates and time in microseconds from some origin such as Mar. 1, 1900 and we are good (as far as dates, but without the time of day) until some time
Effect of superficial gas velocity on the particle temperature distribution in a fluidized bed with heat production
The heat transfer behavior of particles and gas in an olefin polymerization fluidized bed was numerically analyzed using an in-house developed 3-D computational fluid dynamics discrete element model (CFD-DEM). First the implementation of the model was verified by comparing simulation results with analytical results. A constant volumetric heat production rate was implemented in the particle energy equation to mimic the heat production due to the polymerization reaction. It was found that the probability density function (PDF) of the particle temperature becomes more homogeneous with increasing superficial gas velocity. Furthermore, instantaneous snapshots of the thermal driving force (the difference between the single particle temperature and bed-average gas temperature, Tp− ) for different heat production rates provide detailed insight in the particle temperature distribution inside the fluidized bed. The time- and bed-averaged particle convective heat transfer coefficient, which was calculated by Gunn׳s correlation, was found to be independent of the superficial gas velocity. This is explained by the fact that the relative velocity of gas and particles in the emulsion phase, where most of the particles and gas interact, is hardly influenced when increasing the gas superficial velocity. From the spatial distribution of Nusselt number, it becomes apparent that the high heat transfer regions are found in the wake of rising bubbles, whereas low heat transfer rates are found in the clouds of the bubbles.