FLOCCULATION OF ASPHALTENES AT HIGH PRESSURE. II. CALCULATION OF THE ONSET OF FLOCCULATION

The influence of pressure on the onset of flocculation of asphaltenes was calculated in the region from 1 to 300 bar and from 50 to 100°C. These calculations are the counterpart to our experimental data which, recently, have been reported in part 1 of an equally titled article [9]. As gas component methane and as precipitant i-octane were used. The asphaltene flocculation was considered to be a liquid-liquid equilibrium. For modelling the van der Waals equation of state (vdW-EOS) in the framework of continuous thermodynamics was applied. The composition of the crude oil was described by a continuous distribution function with respect to the solubility parameter δ of the Scatchard-Hildebrand theory. Within the distribution the asphaltenes represent the species with the highest δ-values. For oils with a very low content of asphaltenes the model developed describes the experimental flocculation data reasonably. In accordance to the experimental data the model predicts that, in the considered pressure range, without addition of i-octane asphaltene flocculation does not occur. However, on contrary to the experimental results, the model predicts the asphaltenes to show a higher flocculation tendency with increasing asphaltene content of the crude oil. For very high asphaltene contents the model even completely fails. Probably, the reason of this lack is the disregarding of asphaltene association.     

Growth structure investigation of MgF2 and NdF3 films grown by molecular beam deposition on CaF2(111) substrates

The growth structure of MgF₂ and NdF₃ films grown on polished CaF₂(111) substrates deposited by molecular beam deposition has been investigated using transmission electron microscopy (TEM) of microfractographical and surface replications as well as cross-sectional TEM, atomic force microscopy, packing density, and absorption measurements. It has been shown that by taking advantage of ultrahigh vacuum environments and a special stratification property of MgF₂ and NdF₃ films, the preparation of nanocrystalline films of high packing density and low optical absorption is possible at a substrate temperature of 425 K.     

Packing-density calculation of thin fluoride films from infrared transmission spectra

Optical thin films of MgF(2) and NdF(3) have been made by molecular-beam deposition in ultrahigh vacuum. The film packing density was calculated from the water amount that filled the cavities of the films in air. For that the transmission in the IR spectral region with a characteristic water absorption band at a wave number of 3400 cm(-1) was measured. The influence on the packing density of a modification of thin-film morphology by stratification of very thin sublayers of different crystallizing fluorides is tested.     

Antireflection coatings for UV radiation obtained by molecular-beam deposition

We have developed fluoride antireflection (AR) coatings on MgF(2) substrates for a wavelength of 248 nm by molecular-beam deposition. Transmission and laser-induced damage threshold of the samples were measured and atomic force microscope (AFM) investigations were carried out. We compare a 14-layer design for AR coatings with sublayer thicknesses of 12 nm with a conventional two-layer design with quarter-wavelength thicknesses. The laser-induced damage threshold of the 14-layer coating is slightly higher than that of the two-layer coating. The AFM surface images show that the 14-layer coating has a smoother surface than the two-layer coating.     

Thirty Years of Monte Carlo Simulations of Electronic Transport in Semiconductors: Their Relevance to Science and Mainstream VLSI Technology

We review briefly some aspects of the history of Monte Carlo simulations of electronic transport in semiconductors. In the early days their heavy computational cost rendered them suitable only to study problems of pure physics, as simpler models provided the answers necessary to design ‘electrostatically good’ devices. Now that scaling has taken another meaning (i.e., looking for alternative materials, crystal orientations, device geometries, etc.), Monte Carlo simulations may gain popularity once more, since they allow an efficient and reliable evaluation of speculative ideas. We show examples of both aspects of the results of Monte Carlo work.     

Lineare versus sprungfixe Erfolgsbeteiligung

Zusammenfassung Der vorliegende Beitrag diskutiert die Gestaltung optimaler Anreizsysteme für zwei Typen von Erfolgsbeteiligungen: die lineare und die sprungfixe Belohnungsfunktion. Im Gegensatz zu der üblichen Annahme der Principal-Agent-Theorie einer einmaligen Realisation eines Projekts betrachten wir die spezielle Situation, daß eine mehrmalige Wiederholung eines bestimmten Projekttyps in gleicher Form möglich ist. Es wird gezeigt, daß für den Fall der Risikoversion des Entscheidungsträgers und Risikoneutralität der Instanz die sprungfixe Belohnungsfunktion gegenüber der linearen Belohnungsfunktion von Vorteil sein kann.Wir danken einem anonymen Gutachter für wertvolle Verbesserungsvorschläge.     

Amplitude-modulated laser imager

Laser systems have been developed to image underwater objects. However, the performance of these systems can be severely degraded in turbid water. We have developed a technique using modulated light to improve underwater detection and imaging. A program, Modulated Vision System (MVS), which is based on a new theoretical approach, has been developed to predict modulated laser imaging performance. Experiments have been conducted in a controlled laboratory environment to test the accuracy of the theory as a function of system and environmental parameters. Results show a strong correlation between experiment and theory and indicate that the MVS program can be used to predict future system performance.     

Demodulation techniques for the amplitude modulated laser imager

A new technique has been found that uses in-phase and quadrature phase (I/Q) demodulation to optimize the images produced with an amplitude-modulated laser imaging system. An I/Q demodulator was used to collect the I/Q components of the received modulation envelope. It was discovered that by adjusting the local oscillator phase and the modulation frequency, the backscatter and target signals can be analyzed separately via the I/Q components. This new approach enhances image contrast beyond what was achieved with a previous design that processed only the composite magnitude information.     

A narrow-channel, 0.2-μm gate-length, double-quantum-wellpseudomorphic MODFET with high power gain at millimeter-wave frequencies

State-of-the-art pseudomorphic MODFETs were developed with metallurgical gate lengths between 0.22 and 0.25 μm, very short source-to-drain spacings of 0.7 μm, and a double-quantum-well material structure. S-parameter measurements were performed on these 60-μm gate-width devices up to 40 GHz. From these S-parameter measurements, an extrapolated value of 82 GHz was estimated for F_t. Modeling of the power gain as a function of frequency indicates that F_max may be as high as 305 GHz     

Moisture content in honey determination with a shear ultrasonic reflectometer

An ultrasonic method, based on the measurement of the complex reflection coefficient at an interface (elastic material)/(viscoelastic material) has been developed for shear waves and an operating frequency of 10 MHz. With this technique, the dynamic elastic moduli G′ and G′′ can be obtained with a high accuracy. For various honeys and moisture contents we show that the temperature for which (G′′/G′) = 1 undergoes an important variation (25–3 °C) for moisture contents ranging from 15% to 20%. With this technique one can distinguish two honeys with moisture contents difference less than 0.2%. Regarding the high sensitivity of the method, considering the fact that ultrasonic waves can propagate through optically opaque materials and is a nondestructive approach, we propose a discussion about the application of this technique for honey quality control.