Silver halide-containing photochromic powders of SiO2 sol–gel glass

In order to develop a photochromic powder, an SiO2-gel based on tetraethoxysilane (TEOS) was doped with AgNO3 or AgNO2. The dried gel pieces were pulverized and treated with aqueous or ethanolic halide solutions for growing silver halide microcrystals. Both the introduction of cuprous compounds such as CuBr, CuCl, Cu2O, Cu(CH3COO)2·H2O or sulphur-containing compounds and the formation of AgBrxCl1-x crystals lead to variations of photochromic properties. X-ray diffraction measurements indicate that the average diameters of silver halide microcrystals are limited to 70–110nm. Ultraviolet–visible spectroscopic investigations show the reversibility of the darkening/fading process. Cu+-containing samples exhibit a remarkable fading even at room temperature.     

Observability and ε-observability for distributed-parameter systems

The aim of this article is to study the observability and state reconstruction of parabolic systems. It is shown that observability can be deduced from the coercivity of a bilinear form associated with a quadratic criterion, and that the solution depends continuously on the data. The regularization of the criterion enables the notion of ε-observability of parabolic systems to be introduced, and the relationships between the two notions are studied. The practical case of systems of finite dimension obtained by discretization of continuous equations is also studied, from the point of view of observability as well as ε-observability and the results obtained, and numerical examples are provided to indicate why it may be of interest to search a priori for an ε-observation in applications.     

FAST S-PARAMETER COMPUTATION OF A MICROSTRIP INTERDIGITAL FILTER USING TLM,PRONY'S AND DIGITAL FILTERING TECHNIQUES

A spectral estimation technique based on Prony's method has been used to analyse a five section microstrip interdigital filter with the TLM method. The time response of the filter is expressed as the sum of only five damped sinusoids, yielding an analytical expression for the time response. Furthermore, since an analytical Fourier transform exists for this expression, the frequency response is obtained without applying the fast Fourier or discrete Fourier transform. This typically reduces the time required for a TLM analysis by a factor of five. The approximation agrees very well with a full TLM time response. It is also shown that the numerical noise due to single precision computation of the absorbing boundary algorithm can be eliminated by digital filtering techniques. The effect of the via holes used for grounding the quarter-wave resonators of the filter has been included by discretizing them along with the rest of the circuit. Scattering parameters for the filter compare well with measurements published by Swanson.     

Methods for classification of two thyroid follicular tumour classes

The goal of the present paper is to show that certain cytometric (morphological, photometric and textural) features of isolated cell nuclei can be useful for discrimination and classification of two thyroid tumour classes, namely, follicular adenoma and follicular carcinoma which cannot in general be visually discriminated in cytological smears. Several linear classifiers both at cell and specimen levels are proposed, in order to estimate the true error rate of these classifiers, a ‘hold one specimen out’ scheme is employed.     

FREE CONVECTIVE DRAFT INDUCED BY THERMAL AND CONCENTRATION GRADIENTS INSIDE AN ISOTHERMAL,VERTICAL CYLINDER†

Laminar, free convective flow through a vertical cylinder induced by the thermal and concentration buoyancy forces is investigated. The numerical studies involve development of a steady-state, two-dimensional heat and mass transfer model for the moist air core of the vertical tube. The stream function-vorticity method is employed to simplify the governing, coupled conservation equations which were then numerically solved by the successive over-relaxation (SOR) and alternating direction implicit ((ADI) methods.

A graphical correlation was found between dimensionless flow rate and dimensionless tube length as a function of the buoyancy force ratio N = Gr/Grc. Excellent agreement was obtained for the dimensionless flow rale results with those of Davis and Perona¹⁶ and Kageyama and Izumi¹³ for the case when only the-thermal buoyancy force is considered.

The combined buoyancy force from thermal and species diffusion provides larger local Nusselt Nu and local Sherwood Sh numbers relative to the case when just one buoyancy force is accounted for. Both local Nu and local Sh are seen to asymptotically approach a constant value as flow develops.     

MELTING OF ICE AROUND A HORIZONTAL ISOTHERMAL CYLINDRICAL HEAT SOURCE

Processes during melting from a horizontal cylindrical heat source of uniform surface temperature embedded in ice have been studied experimentally. The volume of the melt and its shape were photographed at different times for various constant temperatures of the heat source. At early times and under all conditions, the melt occupied a cylindrical annulus. At later times free convective motion caused pear-shaped melt contours which pointed downward when the temperatures of the heat source were below 7°C and upward when the temperatures were above 8°C. Instabilities in cellular natural convection motion resulted in waviness of the interface. The location and magnitude of these ripples were found to depend on the temperature of the heat source and the melt layer thickness. Shadowgraph techniques were used to determine local heat transfer coefficients at the heat source surface.     

Specific intentions–general realities: on the relation between urban forms and political aspirations in Berlin during the twentieth century

Berlin as a capital city seems to be a very specific case: no other capital city experienced political changes as extreme as Berlin in the twentieth century. All the different political systems tried to impose their political aspirations on the urban fabric, planning large government complexes with specific urban images and highly political overtones. Therefore, the planning history of Berlin is often considered as unique – each phase of planning belonging closely to the political body that installed it – and each phase of planning being part of a special Berlin planning history.

Within this article Berlin's planning history is interpreted in a different way. First, there are planning ideas, which are far more constant than the political systems and which cannot be attributed to only one system. Secondly, for each planning idea which had been developed for special political purposes in Berlin, some international examples can be found which root it in an international urban debate rather than in a regional tradition. The result is quite astonishing, since for nearly every plan international examples with often contradictory political ideas can be found. This means that one can no longer interpret Berlin's planning history as a special case, explainable mostly by local traditions and political intentions. In fact, urban design for government districts in Berlin is more closely connected to international trends and the discipline of urban design. Thus, in addition, the relationship between urban forms and political aspirations must be considered as being more arbitrary than conventionally seen.     

Calculation of the inversion channel resistance for n-MOSFETs using a classical and semi-quantum-mechanical model

Two models are presented to calculate the inversion channel carrier distribution of an n-type MOSFET. The classical approach solves Poisson's equation and applies Fermi-Dirac statistics in conjunction with Gauss's law to determine the carrier distribution. The semi-quantum-mechanical model solves Schrodinger's equation decoupled from Poisson's equation and the Fermi-Dirac statistics by assuming a constant electrostatic field and quantized energy levels. The results of both models are used to determine the channel resistance taking transversal field initiated mobility reductions into account. A comparison is made to a practical device and the results discussed.     

Dilatation Behavior of Two Differently Heat-Treated Commercial Magnesia-Partially-Stabilized Zirconias

The dilatation behavior of two grades of partially stabilized zirconia (PSZ) was determined. ZN 40 is a material which contains 40% to 50% t -ZrO₂ particles, and has a reproducible dilatometric behavior up to 900°C. ZN 50 is a Mg-PSZ containing 20% to 30% of the monoclinic phase. The cyclic dilatation curves show an unstable hysteresis effect which arises from the tetragonal-monoclinic phase transformation.     

Viscosity-Drift Technique for Determination of Critical Liquid-Liquid Immiscibility Temperature of Glasses

The time dependence of the low-temperature viscosity was used to determine the occurrence of phase separation in glass systems and to measure the critical immiscibility temperature. The technique is fast and easily performed and can be applied to materials with very low immiscibility gaps. Immiscibility temperatures for several technically important glass compositions are given.