Single-frequency, single-knob tuning of a CW color center laser

We describe a simple way to achieve CW single-frequency laser operation with a grating as the sole tuning element. It is Shown, both experimentally and theoretically, that by proper choice of cavity parameters, the competing hole burning modes can be completely suppressed. Experiments to demonstrate the theoretical calculations were carried out in a CW color center laser using Tl⁰(1) centers. Linewidths of 0.01 cm^-1were obtained and this figure can probably be much improved by proper cavity stabilization. The method can be readily extended to any compact gain medium.     

Why is software late? An empirical study of reasons for delay insoftware development

A study of the reasons for delay in software development is described. The aim of the study was to gain an insight into the reasons for differences between plans and reality in development activities in order to be able to take actions for improvement. A classification was used to determine the reasons. 160 activities, comprising over 15000 hours of work, have been analyzed. The results and interpretations of the results are presented. Insight into the predominant reasons for delay enabled actions for improvements to be taken in the department concerned. Because the distribution of reasons for delay varied widely from one department to another, it is recommended that every department should gain an insight into its reasons for delay in order to be able to take adequate actions for improvement     

Dynamical considerations of network properties

Elasticity is discussed as an aspect of viscoelasticity, which is described by the tube model. The effects of both crosslinks and entanglements contribute to this model and a discussion of how these effects can be quantified is given. At high enough concentration, entanglements ensure the existence of elastic effects even without crosslinks, and a theory is presented on how this dynamical phase change comes about.     

Molecular correlations in sheared thermotropic copolyesters showing banded textures

Banded textures produced in a thermotropic liquid crystal polymer by shearing between glass slides are examined by using both transmission electron and polarized light microscopy. The periodic variation in director orientation about the shear axis, as measured by light microscopy, is shown to be distinctly different from that indicated by electron diffraction. Measurements of birefringence and observation of Zernicke phase contrast indicate periodic variations in optical properties of the polymer, in step with the bands. Such effects are accounted for in terms of a synchronous rotation of the planar aromatic groups about the molecular chain axes. Evidence for an out-of-plane component of molecular orientation is also presented.     

The effects of pressure on the isothermal fluid behavior of bituminous coals

An investigation into the effects of pressure (helium gas) on the isothermal fluid behavior includes: (1) the effect of pressure on the rate of melting and coking as evidenced by the rate constants k(melt) and k(coke); (2) the effect of pressure on the energies of activation of melting and coking; (3) the effects of pressure on the characteristic times; (4) the effects of pressure on the maximum isothermal fluidity. Results from the effects of pressure on k(melt) revealed that it was generally the high total sulfur, low nitrogen, low reactives/mineral matter ratio, medium rank coals which show the greatest increase in k(melt), whereas the highest rank coals show the least decrease in k(coke). The energies of activation of melting and coking were not significantly affected by pressure. The investigation also reveals increases or decreases in the respective times of softening, maximum fluidity, resolidification and total time of fluid behavior under isothermal pressurized conditions. There appears the possibility that these shifts may be rank dependent. Additionally, the lower rank coals show the largest relative increase in their fluidities when subjected to pressure. Empirical relationships were derived in order to quantitatively predict the maximum isothermal fluidity for most (fluid) coals at a given pressure.     

New phenothiazine dyes and pigments

The synthesis of three new azaphenothiazine ring systems and an evaluation of their use as intermediates for new dyes and pigments is described. 2-Amino-5-bromopyrazine-3[4H]-thione (11) was prepared and converted to the novel 1,4,6,9-tetraazaphenothiazine ring system. The reaction of 4,5-diaminopyrimidine-6[1H]-thione (15) with 2,3-dichloropyrazines gave the isomeric 1,4,6,8-tetraazaphenothiazine ring system, another new heterocycle in this series. With 2,3-dichloroquinoxaline a previously unknown tetracyclic tetraazaphenothiazine ring system was isolated in satisfactory yields. The properties and reactions of these new heterocyclic systems are presented. Mixed nitric and sulphuric acids convert them to their 5-sulphoxides. Structural assignments were based on chemical evidence and their UV, IR, NMR and mass spectra. Mechanistic pathways to these compounds are also proposed.     

Constant stretching rate experiments on low density polyethylene

A simple apparatus for elongational test of molten polymers is presented. Its realiability is demonstrated by means of stress growth in constant stretching rate experiments and relaxation test on a low density polyethylene sample.     

Reconstruction of polygonal sets by constrained and unconstrained double probing

The problem of recovering the shape of planar objects arises in robotics. This work deals with this problem under the assumption that composite double probings are made. Two kinds of double probes are considered and their use for reconstructing convex planar polygons is investigated. For both kinds of probes, lower bounds on the number of probings required for reconstruction under any strategy are obtained and specific strategies which are proven to be almost optimal are provided.     

Neural networks-then and now

The emergence of neural networks as a significant subdiscipline with corresponding attempts at application to engineering problems is traced back to the 1960s, when Frank Rosenblatt, a Cornell University psychologist, showed by mathematical analysis, digital computer simulation, and experiments with special-purpose parallel analog systems that neural networks with variable-weight connections could be trained to classify spatial patterns into prespecified categories. In his attempts to provide biologically plausible explanations of the function of the central nervous system, he investigated relatively simple networks that were amenable to analysis and more complex networks whose behavior could be predicted only in terms of gross characteristics. He assembled a sizable group involving theoreticians, experimentalists, technologists, and, later, biologists. His work caught the imagination of the press and led to the wave of febrile activity that subsided at the end of that decade.     

Asymptotic analysis of queues in multiple-access computer networks

The paper considers local-area computer networks with a protocol that supports carrier-sense multiple access with instantaneous conflict detection and is a generalization of slotted ALOHA. An approach based on recurrent processes is applied to analyze the asymptotic behavior of the number of waiting calls under conditions of low retrial rate.Translated from Kibernetika i Sistemnyi Analiz, No. 4, pp. 54–61, July–August, 1991.