Reliability Evaluation by Network Decomposition

The method evaluates the reliability of large computer communication systems by systematic decomposition of the probabilistic graph of the system into two parts using an appropriate cutset. A technique is evolved for determining the conditional success events using both the node removal and connection multiplication methods for path enumeration. An example is solved to show the versatility of the method. The results of the example are verified by using an existing algorithm. The suggested method is general and computationally economical.     

Modification of cutsets for reliability evaluation of communication systems

A general and simple technique for the evaluation of symbolic reliability expression in the case of practical systems such as a communication system having fixed channel capacities of its various communicating links, a computer communication network allowing a fixed amount of data exchange amongst different terminals of various computer centres and a power distribution system having limited power ratings of its various power lines, is presented. A system is considered reliable only if it successfully transmits at least the required system capacity from the transmitter to the receiver station. In this method, the various branch sets are obtained which completely disrupt the communication path, i.e. ensure system failure. It is observed that these branch sets are not necessarily the cutsets in the usual graph theoretic sense. The unreliability expression is then determined by adopting an existing method for making various terms disjoint. Two typical examples are solved by this method. It is observed that the method is computationally fast and efficient.     

Structure from motion of rigid and jointed objects

A method for recovering the three-dimensional structure of moving rigid and jointed objects from several single camera views is presented. The method is based on the fixed axis assumption: all movement consists of translations and rotations about an axis that is fixed in direction for short periods of time. This assumption makes it possible to recover the structure of any group of two or more rigidly connected points. The structure of jointed objects is recovered by analyzing them as collections of rigid parts, and then unifying the structures proposed for the parts. The method presented here has been tested on several sets of data, including movies used to demonstrate human perception of structure from motion.     

Highly Sensitive Pulsed Digital Holography for Built-in Defect Analysis with a Laser Excitation

A highly sensitive method is presented for noninvasive defect analysis on thin structures with a Q-switched double-pulsed ruby laser with frequency doubling (347 nm). In our research we feature an all-optical arrangement, where a focused laser pulse derived from the same ruby laser (694 nm) acts as a built-in synchronous excitation source for digital holographic interferometry. The recordings are made with a CCD camera for capturing two holograms (two states of the specimen) corresponding to the two UV laser pulses with a short time separation (10-50 mus). Subtraction of the phase distribution in two digital holograms gives a fringe phase map that shows the change in deformation of the specimen between the recordings. The advantage of the proposed method is two fold. First, the use of a shorter wavelength results in a higher sensitivity. Second, owing to the induced synchronous built-in optical excitation, the specimen is not subjected to any external physical excitation devices. Experimental results are presented on identification and evaluation of defects in thin metal sheets.     

Effect of calcination conditions of self-sintering mesocarbon microbeads on the characteristics of resulting graphite

Mesocarbon microbeads are now-a-days used as a prominent self-sintering precursor for the production of high density monolithic graphite. The quality of this graphite is highly dependent on the characteristics of these microbeads, such as the quinoline and toluene insoluble contents, -resins content and volatile matter content, which in turn, can be controlled to desired values by suitable treatments of their extraction and calcination. In the present paper, the authors give an account of the study conducted to see the effect of calcination conditions of mesocarbon microbeads on the characteristics of the resulting graphite. A calcination at a temperature in the range of 280–320 °C for 30 min. under an ambient pressure of nitrogen, or at a temperature of 245–310 °C for 10 min. under a reduced pressure (5 cm Hg) of nitrogen, results in mesocarbon microbeads having a quinoline insoluble content of 83.6–89.8%, toluene insoluble content of 94.4–99.7%, -resins content of 6.8–11.9% and a volatile matter content of 10.2–13.5%. Such microbeads have been found to lead to a monolithic graphite possessing a bulk density 1.91–2.02 g cm^–3, bending strength of 62–70 MPa, Shore hardness of 58–69, electrical resistivity of 2.1–2.6 m cm and a degree of anisotropy of 1.02–1.05.     

Impedance studies of polycrystalline tin oxide

Polycrystalline SnO₂ samples prepared in the laboratory were irradiated with 2 MeV He ions having doses of 3.62 × 10¹⁵ ion/cm². The ac small-signal electrical data acquired for the polycrystalline SnO₂ in the frequency (f) range 100 Hz ≤ f ≤ 1 MHz and temperature (T) range 26°C ≤ T ≤ 100°C revealed one semicircular relaxation in the impedance plane for the He implanted sample. However, two semicircular relaxations were obtained in the same plane for the samples without He implantation. The He implantation indicated enhancement in the donor density in the polycrystalline SnO₂ as depicted via terminal conductance (or resistance). An erratum to this article can be found at     

Cryogenic Yb3+-Doped Solid-State Lasers

Cryogenically cooled solid-state lasers promise a revolution in power scalability while maintaining a good beam quality because of significant improvements in efficiency and thermo-optic properties. This is particularly true for Yb lasers because of their relatively low quantum defect and relatively broadband absorption even at cryogenic temperatures. Thermo-optic properties of host materials, including thermal conductivity, thermal expansion, and refractive index at low temperature, are reviewed and data presented for YAG (ceramic and single crystal), GGG, GdVO₄, and Y₂O₃. Spectroscopic properties of Yb:YAG and Yb:LiYF₄ (YLF) including absorption cross sections, emission cross sections, and fluorescence lifetimes at cryogenic temperatures are characterized. Recent experiments have pushed the power from an end-pumped cryogenically cooled Yb:YAG laser to 455-W continuous-wave output power from 640-W incident pump power at an of M² 1.4.