TWO ALPHA F1SCHER-TROPSCH PRODUCT DISTRIBUTION. A ROLE FOR VAPOR-LIQUID EQUILIBRIUM?

The simple polymerization mechanism for the Fischer-Tropsch synthesis produces products which follow an Anderson-Schulz-Flory distribution. Thus, plotting the logarithm of the mole fraction versus carbon number produces a straight line whose slope is related to alpha which is determined by the chain termination and propagation probabilities. In contrast, the products from laboratory and large commercial plants exhibit a two-alpha plot. Vapor-liquid calculations show that product accumulation cannot be responsible for the two-alpha plot when the alpha value is large enough to produce liquid products at the reaction temperature. Only in the case where alpha is small and all products are in the vapor phase, allowing evaporation of the startup solvent and a “drying out” of the reactor, can product accumulation produce a two-alpha plot.     

Prediction of net-length distribution for global interconnects in aheterogeneous system-on-a-chip

A system-on-a-chip (SoC) contains several pre-designed heterogeneous megacells that have been designed and routed optimally. In this paper a new stochastic net-length distribution for global interconnects in a nonhomogeneous SoC is derived using novel models for netlist, placement, and routing information. The netlist information is rigorously derived based on heterogeneous Rent's rule, the placement information is modeled by assuming a random placement of terminals for a given net in a bounding area, and the routing information is constructed based on a new model for minimum rectilinear Steiner tree construction (MRST). The combination of the three models gives a priori estimation of global net-length distribution in a heterogeneous SoC. Unlike previous models that empirically relate the average length of the global wires to the chip area, the new distribution provides a complete and accurate distribution of net-length for global interconnects. Through comparison with actual product data, it is shown that the new stochastic model successfully predicts the global net-length distribution of a heterogeneous system     

A tribute to D.B. Spalding and his contributions in science and engineering

This paper presents a summary of some of the scientific and engineering contributions of Prof. D.B. Spalding up to the present time. Starting from early work on combustion, and his unique work in mass transfer theory, Spalding’s unpublished “unified theory” is described briefly. Subsequent to this, developments in algorithms by the Imperial College group led to the birth of modern computational fluid dynamics, including the well-known SIMPLE algorithm. Developments in combustion, multi-phase flow and turbulence modelling are also described. Finally, a number of academic and industrial applications of computational fluid dynamics and heat transfer applications considered in subsequent years are mentioned.     

Slender Monumental Stair Vibration Serviceability

This paper presents the results of an experimental and analytical study of a slender monumental stair. The objective of the study was to gain insight into slender stair vibration issues and provide guidance for the design of such stairs. A slender monumental stair was vibration tested to estimate modal properties and acceleration due to walking. A detailed unadjusted finite-element model was created of the stair using only information that would be available to a designer. The model was used to predict the modal properties and accelerance magnitude. The accelerance magnitude was then used with established harmonic footstep forces to predict the steady-state acceleration due to walking. A factor was developed to account for imperfect resonant buildup, providing reasonable predictions of acceleration due to walking. Design forces were derived based on a set of stair ascent and descent footstep force measurements. An absolute minimum natural frequency is recommended for vertical and horizontal vibrations. Practical aspects of stair vibration analysis are discussed, including the handling of group loading, likely affected occupant locations, and guardrail lateral vibration.     

Synchronized chaotic mode hopping in DBR lasers with delayedopto-electric feedback

We propose and demonstrate a scheme for generating synchronized chaotic mode hopping in two wavelength-tunable lasers. Chaotic mode hopping resulting in large hops in wavelength is induced by delayed feedback of an electrical signal proportional to the intensity of the laser output which passes through an optical filter. Mode hopping among up to 11 modes was experimentally observed and optical signals in each wavelength band show a different on-off modulation time series. Analysis of the time series indicates high dimensionality. By using a unidirectional coupling method that injects part of the output of one laser into another, we can synchronize the chaotic mode hopping of two separate lasers and obtain synchronized chaotic on-off modulation patterns in multiple corresponding wavelength bands. The robustness of the synchronization with respect to the parameter mismatch and the effects of the coupling strength are investigated. The chaotic mode hopping dynamics and synchronization are well described with a numerical model that includes the characteristics of the laser tuning and the filter transmission. A multiplexed data transmission scheme using chaotic carriers is proposed and experiments demonstrate that multiple messages can be simultaneously recovered when chaos synchronization is achieved     

Interconnect limits on gigascale integration (GSI) in the 21stcentury

Twenty-first century opportunities for GSI will be governed in part by a hierarchy of physical limits on interconnects whose levels are codified as fundamental, material, device, circuit, and system. Fundamental limits are derived from the basic axioms of electromagnetic, communication, and thermodynamic theories, which immutably restrict interconnect performance, energy dissipation, and noise reduction. At the material level, the conductor resistivity increases substantially in sub-50-nm technology due to scattering mechanisms that are controlled by quantum mechanical phenomena and structural/morphological effects. At the device and circuit level, interconnect scaling significantly increases interconnect crosstalk and latency. Reverse scaling of global interconnects causes inductance to influence on-chip interconnect transients such that even with ideal return paths, mutual inductance increases crosstalk by up to 60% over that predicted by conventional RC models. At the system level, the number of metal levels explodes for highly connected 2-D logic megacells that double in size every two years such that by 2014 the number is significantly larger than ITRS projections. This result emphasizes that changes in design, technology, and architecture are needed to cope with the onslaught of wiring demands. One potential solution is 3-D integration of transistors, which is expected to significantly improve interconnect performance. Increasing the number of active layers, including the use of separate layers for repeaters, and optimizing the wiring network, yields an improvement in interconnect performance of up to 145% at the 50-nm node     

Highly ordered uniform single-crystal Bi nanowires: fabrication and characterization

A mechanical pressure injection technique has been used to fabricate uniform bismuth (Bi) nanowires in the pores of an anodic aluminum oxide (AAO) template. The AAO template was prepared from general purity aluminum by a two-step anodization followed by heat treatment to achieve highly ordered nanochannels. The nanowires were then fabricated by an injection technique whereby the molten Bi was injected into the AAO template using a hydraulic pressure method. The Bi nanowires prepared by this method were found to be dense and continuous with uniform diameter throughout the length. Electron diffraction experiments using the transmission electron microscope on cross-sectional and free-standing longitudinal Bi nanowires showed that the majority of the individual nanowires were single crystalline, with preferred orientation of growth along the [011] zone axis of the pseudo-cubic structure. The work presented here provides an inexpensive and effective way of fabricating highly ordered single-crystalline Bi nanowires, with uniform size distributions.     

Effects of kraft mill effluents on juvenile salmon production in laboratory streams

Effects of effluents on juvenile chinook salmon Oncorhynchus tshawytscha were studied in six laboratory streams. Primary effluent (KME) from mill A reduced salmon production at a concentration of 1.5% by volume (0.2 × 96h TL50) but not at 0.5% (0.07 × 96 h TL50). Fall and spring exposure to stabilized kraft effluent (SKME) from mill A at 1.5% reduced salmon production, while in summer experiments, fish production was enhanced at concentrations of up to 4% for mill A and up to 7.5% for mill B. Thus, production values varied with the source and extent of treatment of effluent and perhaps with season. Fish growth was related to food density during some experiments.     

High-power etched-facet lasers

We demonstrate, for the first time, laser diodes with anetched facet fabricated by chemically assisted ion beametching, producing 1?7 W pulsed and 470mW CW output power from one facet. The devices were coated and bonded junction-side-up and tested at room temperature. The single 40 ?m stripe, 300 ?m-long devices exhibit 94 mA threshold current and differential quantum efficiencies of 80% pulsed (78% CW).