Not the least interesting of the many remarkable properties of diamond is that it emits visible light on excitation by appropriate methods.Many investigators have studied the luminescence of diamond since Robert Boyle in 1663 published his observations of the phenonienon. To the methods of exciting luminescence described by him, viz., light, heat and friction, the advance of knowledge has added others, viz., cathode-ray bombardment and X-rays. It has also provided instruments, viz., the phosphoroscope and the spectroscope for the critical study of the phenomenon and extended the range of temperatures over which it maybe. observed downwards to the lowest values. A full summary of the earlier investigations is given in the fourth volume of Kayser's Handbuch (1908). In view of the fact that diamond is an elementary solid and is the typical valehce crystal, it mi&t have been supposed that its behaviqur would figure prominently in any account of the subject of luminescence. Far from this being the case, the luminescence of diamond does not even find a mention in the two bulky treatises written by Lenard for the Handbuch der Experimental Physik, or in Pringsheim's article of 1928 in the Handbuch der Physik.
The reason for this lack of interest is clear from the brief reference thade in Pringsheim's book (1928) and in his earlier Handbuch article (1926), namely the belief that the centres of luminescence in diamond are not the atoms of carbon of which it is composed, but some foreign atoms of undetermined identity present in it as impurity. The basis for this belief has been the variability of the intensity and colour of the emitted light, and the fact that not all diamonds show the phenomenon. The impurities suggested in the literature as the origin of the luminescence make a lengthy list, viz., samarium, yttrium, sodium, aluminium, chromium, iron and titanium, and include even some hydrocarbons! The considerations regarding the crystal symmetry and structure of diamond developed in the introductory paper of this Symposium (Raman 1944) enable us to make a fresh approach to the problem of its luminescence. It is proposed to give a general outline of the experimental facts regarding the luminescence properties of diamond and to show that they fit naturally into the framework of the ideas developed in that paper, while, on the other hand, the facts remain wholly unintelligible on the impurity hypothesis.
This PDF Ebooks is an attempt to address the phenomenon of the sun in architecture. Particular use is made of the notions of warmth, light, shadow and energy as form generators. Of specific concern is how one structure can work in harmony within its environment and existing constraints.
An analysis of an existing building is performed, with an eye to its strengths and weaknesses as a residence. It is an interesting challenge for an architect to take an undistinguished building - one designed for a bygone age of surplus energy - to identify those substantive elements to be retained and reused, those which are to be eliminated or substantially altered, and then harmonize them, in conjunction with a new plan, in order to create a warm, energy efficient, aesthetically appealing, and ultimately livable family residence. The possibilities concerning the highest and best changes to be made to improve the use of an existing structure are first identified.
Although non-financial corporate debt (bond issues and privately issued debt) has become more common in the past 10-20 years, bank loans are still the prime source of business finance, especially for small and medium-sized enterprises (SMEs). As a consequence, banks’ ex-ante assessment of the riskiness of loan applicants and the resulting decision to grant credit (or not) at some risk-adjusted interest rate, is of great importance for businesses. Bank regulators increasingly lean on the risk assessments made by banks: in the Basel Committee’s proposal for new capital adequacy rules, the so called Basel II Accord, internal risk ratings produced by banks have been given a prominent role.
Unlike previous regulation, the rules of Basel II will make the size of the required buffer capital contingent on a bank’s appraisal of ex-ante individual counterpart risk. It will be up to each bank to characterize the riskiness of the counterparts and loans in its portfolio by means of a relatively small number of risk categories or ”rating classes”. A special feature of the new regulation is that retail credit and loans to SMEs will receive a different treatment than corporate loans and will require less regulatory capital for given default probabilities. The main reason for this differential treatment is the supposedly low correlation between small business loans. Their risk is generally thought to be largely of an idiosyncratic nature.
