A key intermediate in the platinum-mediated hydrodesulfurization of dibenzothiophene

The thiaplatinacycles, [PtL2(C,S–C₁₂ H₈S)] and [PtL₂(C,S–C₁₃H10S)] (L = PEt₃, PMe₃; L₂=Ph₂PCH₂ CH2PPh₂), obtained from oxidative insertion of [Pt⁰Ln] into dibenzothiophene and 4-methyldibenzothiophene are hydrodesulfurized by reaction with hydrogen (toluene, 20 atm, 100°C) to biphenyl and 3-methylbiphenyl, respectively; addition of acidic alumina improves the reaction. These observations link the model systems and the latest generation of commercial second-stage HDS catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

INFOREX-3.0: A database on experimental studies of phase equilibria in igneous rocks and synthetic systems: I. Datafile and management system structure

INFOREX-3.0 is a sophisticated database manager for igneous petrologists and geochemists. It is designed as an aid in searching the published experimental database, and extracting specific subsets of that data. In addition, the program allows the user to derive numerical mineral-melt expressions based on any dataset. Its major function is as a computerized melting-experiment reference manual that presents data in a fixed format, with key word search functions and flags as an integral part of the program. At present, the system accesses information on 162 experimental studies carried out from 1962 to 1994. The database includes 6174 individual runs with more than 8300 coexisting phase compositions for 30 minerals plus melt. Most of the data are “dry”, but about 2200 include volatile components, such as H₂O and CO₂. INFOREX is hot-key driven, allowing users to sort easily and quickly through the data using any set of experimental conditions or rock type parameters. The main options include: (1) configuration of INFOREX; (2) extraction of general information on the current state of the system; (3) updating and editing the database files; (4) selection of run conditions of interest (setting rock types plus a range of pressures, temperatures, oxygen fugacities, run duration as well as types of containers and resultant phase assemblages); (5) setting phase assemblages (e.g., olivine-melt or garnet-spinel) for the selected set of experiments; (6) export/import operations; and (7) calculation of mineralmelt geothermometers. The INFOREX database is a powerful tool for the use in the development of petrogenetic models by providing the ability to manipulate easily accessed mineral-melt equilibria data.     

On the Simulation of Unsteady Flow of an Oldroyd-B Fluid by Spectral Methods

We report numerical results on the simulation of unsteady flow of an Oldroyd-B fluid by spectral element methods. Several techniques to cure the instabilities are considered.     

Cybercampuses: design issues and future directions

In recent years, the usage of 3D cyberworlds for educational purposes has increased. The metaphors behind the visual design of such cyberworlds are quite diverse, from replication of real universities, art museums and scientific labs to non-existing fictitious places. In this paper, we focus specifically on “cybercampuses”, i.e. virtual worlds representing real educational institutions such as universities and schools. Based on the results of a case study that we have performed, this paper provides an initial set of requirements for a cybercampus representing an existing university. In this connection, we analyze place metaphors and associated design features of the Virtual Campus of Nanyang Technological University in Singapore, discuss the correspondence between the identified metaphors and associated educational goals, and provide directions for further development. Finally, we outline the major challenges for the future evolution of cybercampuses in the context of organizational, social and technological development.     

Hot electron induced degradation of undoped AlGaN/GaN HFETs

This work presents the effects of hot electron stress on the degradation of undoped Al_0.3GaN_0.7/GaN power HFET’s with SiN passivation. Typical degradation characteristics consist of a decrease in the drain current and maximum transconductance, an increase in the drain series resistance, gate leakage and a subthreshold current. Degradation mechanism has been investigated by means of gate lag measurements (pulsed I-V) and current-mode deep level transient spectroscopy (DLTS). Stressed devices suffered from aggravated drain current slump (DC to RF dispersion) which indicates possible changes in surface charge profiles occurred during hot electron stress test. The DLTS was used to identify the trap creation by hot electron stress. The DLTS spectra of stressed device revealed the evidence of trap creation due to hot electron stress.     

Effect of Temperature Gradient on the Intensity of Light Scattering in Phosphate Glasses in the Glass Transition Range

A correlation between the peak of the intensity of light scattering and the temperature gradient arising across the sample after temperature jumps in the glass transition range is revealed from experimental data. Analysis of the experimental results shows that the peak of the intensity of light scattering is a quadratic function of the temperature gradient. The result obtained is in agreement with the predictions made from the theoretical analysis of the regularities observed in light scattering by nonuniformly heated liquids.     

Surface roughness in final turning: Development of an adequate empirical model

A new method is proposed for empirical modeling. In this approach, the empirical model is improved by the introduction of data from theoretical modeling and experiment design. Comparison of the traditional empirical model and the proposed model shows that the latter is characterized by higher precision, over large ranges of the relevant factors.     

Transverse waves resulting from pulsating instability of two-dimensional flames

We present results of fully compressible Navier–Stokes simulations of pulsating flame instabilities in two dimensions using single-step, first-order Arrhenius kinetics. Model parameters correspond to Zel’dovich and Lewis numbers of Ze = 9.5 and Le = 10, respectively, and flame Mach numbers M_L between 4.62 × 10⁻³ and 2.31 × 10⁻². The results show that the pulsating instability creates two types of transverse waves: deflagrations and detonations. Both types of waves can coexist for the same reactive system, but transverse detonations become more likely as M_L increases. The transverse detonations observed for our model system are of the intermediate type with most of the chemical energy release accompanying the pressure rise. They propagate inside the large preheat zone of the pulsating flame and do not spread into cold material. The results expand our knowledge of possible new phenomena associated with pulsating instability.     

Development of THz-range Gyrotrons for Detection of Concealed Radioactive Materials

The Center for Applied Electromagnetics (AppEl) at the University of Maryland had started development of a sub-THz gyrotron for detecting concealed radioactive materials. The concept is based on the use of a high-power gyrotron whose power being focused in a small spot with dimensions on the order of a wavelength exceeds the threshold level required for initiating a freely localized microwave breakdown in air. However, in the absence of radioactive materials, the ambient electron density is so small that there is a very small probability to find a free electron in this small volume to trigger the avalanche breakdown process. Therefore the fact that the breakdown was observed would indicate that there is a hidden radioactive material in the vicinity of a focused wave beam. We present the design data for a 200?C300 kW, 670 GHz gyrotron operating with a pulsed solenoid and describe a single-shot pulsed solenoid producing 27?C28 T magnetic fields. Also numerous issues in this specific application are discussed, viz. threshold conditions for initiating the breakdown, production of gamma rays by concealed radioactive materials and their role in producing low energy electrons outside a container, wave beam focusing in a small spot by a limited-size antenna, random walk of energetic electrons which may result in appearance of free electrons in a given volume during the RF pulse and comparison of diffusion time with the time required for competing processes, such as ionization and three-body attachment.     

Damage of unfilled crosslinked rubbers as the scission of polymer chains: Modeling and tensile experiments

This article develops a damage model for unfilled crosslinked rubbers based on the concept of scission of polymer chains. The model is built up on the well‐known Gent elastic potential complemented by a kinetic equation describing effects of polymer chain scission. The macroscopic parameters in the damage model are evaluated through the parameters for undamaged elastomer. Qualitative analysis of changing molecular parameters of rubbers under scission of polymer chains resulted in easy scaling modeling the dependences of these parameters on the damage factor. It makes possible to predict the rubber failure in molecular terms as mechanical devulcanization. The model was tested in tensile quasistatic experiments with both the monotonous loading and repeated loading–unloading. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers