Write-once systems

Two naphthalocyanine derivatives (Scheme 9) were mixed together to improve read-out stability in a write-once optical storage system.220 The Ge derivative has a bulky structure with large side chains on the central atom, whilst the Cu derivative has a flat structure. The stability of the medium under 1 mW laser irradiation for read-out was improved 100-fold compared to that of a single-component system.220... 

Heat. As mentioned above most molecules lose energy from the excited state as heat. The most efficient molecules for converting electromagnetic radiation into heat are those that absorb in the near-IR region, i.e., infrared absorbers (IRAs). There has been much interest in IRAs because of their use in laser thermal transfer, optical data storage [the older write-once read-many (WORM) and the newer compact disc recordable (CD-R) and digital versatile disc recordable (DVD-R) systems], computer-to-plate printing, and as solar screens for car windscreens and windows. 

Optical data storage media fall into three main classes [26] (Figure 6.9). Read only media comprise the CD in its audio and CD-ROM formats and DVD, also of the CD format but having about six to ten times the data capacity of a CD-ROM, depending upon whether one or two recording layers are used. These read only media are mainly dedicated to entertainment. As seen from Figure 6.9, the systems which use organic dyes are WORM (write-once-read-many), CD-R, and DVD-R. 

Where copies of electronic documentation and records are provided to an inspector/investigator to take away, they should be provided on read-only media (preferably write-once, read-only). The same issuance process should be followed as for paper documentation (e.g., signed handover of copy to inspector/investigator, and an exact duplicate copy made on the same media as provided to the inspector/investigator for retention by site). Ad hoc electronic reports from computer systems specifically requested during inspections do not have to be validated. ... 

The experimental section is often the easiest to write once you have decided what to report. There may be minor variations in style, but the one shown in Box 52.2 will be suitable in the majority of cases. The results section is the next easiest as it should only involve description. At this stage your should be jotting down ideas for the Discussion - this may be the hardest part to compose, as you need an overview of both your own work and the relevant literature. It is also liable to become wordy, so try hard to make it succinct. The Introduction should not be too difficult if you have understood fully the aims of the experiments. Write the Abstract and complete the list of references at the end. To assist with the latter, it is a good idea to use or pull out their cards from your index system. 

Write once, read many, or WORM systems, are a bit more complicated than ROM systems. Though they have essentially the same optical system for data retrieval, for writing operations they require a more powerful laser and a modified storage disk. 

The problem with the application of these changes in optical properties for optical data storage is that the significant drop in reflectivity upon the first UV irradiation is related to an irreversible structural change. So the film can be used a as write-once medium only. Furthermore, the sensitivity of the system is low, so writing the information takes a rather long time. The changes in the optical properties in subsequent irradiation cycles are reversible, but they are connected with the unstable cis-isomer, which renders the inscribed information volatile. 

Optical information storage, which has been a dream since the discovery of the laser, is now becoming a commercial reality. Read-only consumer products (video and digital audio disks) have provided a solid technological base for the development and introduction of the more sophisticated write-once and erasable recording systems. This chapter will review the current status of polymeric materials as substrates, protective layers, and active recording media in laser recording. 

Several types of Direct Read After Write (DRAW) discs on which data can be digitally recorded either once (write-once) or repeatedly (erasable). Initial applications are largely in professional equipment, for example as storage systems for large archieves. 

The power of PEDOT is its ability to be transformed from a conductor to an insulator by regulating the current which flows through it. The new technology system, which stores more data at less cost than expensive-to-build silicon chips, permits writing once only but allows reading many times. 

In writing Eq. (8.33), we have divided by Nj , since the polymer molecules are interchangeable. Equation (8.33) gives the thermodynamic probabilty for the system according to this model, since there is only one way to place the solvent molecules once the polymer molecules have been positioned on the lattice. 

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