Acetylene formation during the catalytic oxidative dehydrogenation of ethane over Pt-coated monoliths at short contact times

Short contact time monolithic reactors have been examined for the production of ethylene by oxidative dehydrogenation over a supported Ptcatalyst. The results so far suggest that these reactors may revolutionize the way chemical synthesis is conducted, but many questions remain. This paper addresses the co-production of acetylene. Under some conditions, acetylene is produced as a by-product during the oxidative dehydrogenation of ethane. This acetylene formation appears to be due to homogeneous reactions since the acetylene production increases at higher reaction temperatures and under conditions where there is little available surface area for radical quenching. This revised version was published online in July 2006 with corrections to the Cover Date.     

Advantages of an electrical control and energy management system

This paper discusses an electrical control and energy management system (ECEMS) that was installed at Indian Petrochemicals Corporation Limited (IPCL) Nagathone Gas Cracker complex located in Maharashtra, India. This distributed control system (DCS) provided computer assisted control in the areas of: Demand control; Automatic generation control, including MW and MVAR management; Power factor control; Automatic tap changer control; Load shedding; Automatic synchronization of generator and ties; Remote control of breakers. Previously, IPCL, like most other petrochemical companies in India, relied on operator control for power house functions. The process is always automated, but the power house equipment is usually manually controlled. Electrical control and energy management systems are not thought to be necessary. However, in this case the consultants for IPCL and the DCS supplier convinced IPCL that an ECEMS would save them enough money in operating costs to pay for the new control system. The control system discussed in this paper reduced operating costs by satisfying the process steam and power demands in the most cost-effective manner. In addition, the system took action to respond to electrical disturbances, such as loss of tie line and generator tripping, so that stable conditions were restored.     

Degradation of thin oxides during electrical stress

A bond-breaking phenomenon responsible for oxide degradation during electrical stress is considered as a multi-step process that includes generation of precursor breakdown defects by the injected electrons directly in the bulk oxide and the subsequent breakdown of the defect's bonds. Precursor defect generation is attributed to the capture/scattering of the injected electrons by the localized gap states associated with oxide structural imperfections. These precursor defects, represented by significantly elongated Si–O bonds or Si–Si bonds are shown to be unstable due to their vibrational excitation and polarization induced by temperature and an applied electric field, respectively; breakdown of the weak precursor defect's bonds results in the formation of the E^′ centers. The proposed model suggests that new precursor defects are preferentially created in the vicinity of the previously generated E^′ centers. This leads to the formation of defect clusters, which can grow and coalesce throughout the oxide, contributing to oxide leakage current and eventual oxide breakdown. The model describes the charge-to-breakdown dependence on the electron fluence and energy, electric field, temperature and oxide thickness.     

A 3.3-V single-poly CMOS audio ADC delta-sigma modulator with 98-dB peak SINAD and 105-dB peak SFDR

This paper presents a second-order ΔΣ modulator for audio-band analog-to-digital conversion implemented in a 3.3-V, 0.5-μm, single-poly CMOS process using metal-metal capacitors that achieves 98-dB peak signal-to-noise-and-distortion ratio and 105-dB peak spurious-free dynamic range. The design uses a low-complexity, first-order mismatch shaping 33-level digital-to-analog converter and a 33-level flash analog-to-digital converter with digital common-mode rejection and dynamic element matching of comparator offsets. These signal-processing innovations, combined with established circuit techniques, enable state-of-the art performance in CMOS technology optimized for digital circuits     

On the Use of Enterprise Models

This paper presents the results of a field study designed to determine how enterprise models are used. The paper begins with an introduction to enterprise models then provides an overview of the survey method used. No known empirical studies have been conducted to determine how enterprise models actually are used by industry. The research is designed to answer this question. A screening sample and complete web-based survey of 72 enterprise modelers was conducted. The primary research question of this survey was on the use of enterprise models, with particular focus on the three dimensions of living models: scope, enactment, and dynamicity. Half the respondents claim that their enterprise models were of their entire division, multiple divisions, and even multiple enterprises. It is encouraging to see that enterprise models are used on such a wide scope. The enactment of the enterprise models was not as large as was expected. Of the respondents, 75% claimed that their models did not receive information from the enterprise more frequently than quarterly. The same was true for how often the models provided information to the enterprise. Seventy-five percent did not update their models more than five times (although, 32% did update the model three to five times). Finally, additional areas of research are proposed.     

An electrical engineering design course sequence using a top-downdesign methodology

A sequence of two courses (second term of third (junior) year and both terms of fourth (senior) year) has been developed to introduce students to a structured approach to design. The first course includes lecture-style presentation of the top-down, step-wise refinement, design methodology. Realistic documentation and client/consultant communication is fostered as well as the design, fabrication, and testing of a prototype. In the senior-year course, students divide into teams of three members to undertake a single design problem, with individual faculty members acting as “clients”. A more complete sequence of the top-down design process is undertaken in these senior-year projects. Documentation is required at each stage of the design sequence to ensure compliance with the client/team “contract”. Introduction of a formal design process, including time management, has resulted in an increased “success” rate in the final designs and in more complex problems being proposed by the “clients” than had previously been experienced     

The effect of microstructure on microbiologically influenced corrosion

Microbes seem to accelerate the corrosion process. They locate susceptible areas, fix anodic sites, and produce or accumulate chemical species that promote corrosion. The microscopic heterogeneity of many materials—whether created intentionally or as an artifact—is quite clear on the scale of microbes and is an important and overlooked factor in microbiologically influenced corrosion. Weld regions are particularly attractive to microbes in many of the systems studied.     

The expression of stem cell factor and its receptor, c-kit in human endometrium and placental tissues during pregnancy

Stem cell factor (SCF) and its receptor Kit regulate the proliferation and survival of early hematopoietic cell types as well as germ cells and melanocytes. As SCF augments the effects of several hematopoietic growth factors that are produced in reproductive tissues during pregnancy and also plays an important role in cell migration, proliferation, and survival, we studied the expression and localization of this receptor/ligand in human endometrial and placental tissues. Kit was detected by Western blot analysis in early decidual and placental tissues (8-19 weeks gestation) and in term placenta. Immunohistochemistry localized Kit mainly in trophoblast and to a lesser extent in scattered cells in the placental villous core and decidual stroma. Ribonuclease protection assay showed that SCF messenger ribonucleic acid (mRNA) expression increased 3-fold in decidua from early pregnancy compared to proliferative and secretory endometrium (P < 0.05). Placental tissues expressed 4- to 8-fold higher levels of SCF mRNA compared to decidus (P < 0.05). Isolated placental villous core expressed 7-fold higher levels of SCF mRNA than did trophoblast (P < 0.05). Thus, SCF and its receptor Kit are expressed in human endometrium and placental tissues during pregnancy, and the pattern of receptor/ligand expression suggests that endometrial and placental villous core SCF may have a paracrine effect on trophoblast through the receptor Kit.     

Design of sealed cavity microstructures formed by silicon waferbonding

Three fabrication issues related to the design and fabrication of micromechanical devices using sealed cavities within bonded silicon wafers are discussed. The first concerns the resultant residual gas pressure within a sealed cavity between two bonded wafers after bonding and a high-temperature anneal. The second concerns the prediction of plastic deformation in capping layers of single-crystal silicon over sealed cavities. Exposure of sealed cavity structures to a high-temperature environment causes the trapped residual gas to expand, which can result in the plastic deformation of the capping layer. A model for analytically predicting the occurrence of plastic deformatio in these silicon capping layers has been developed. The third fabrication issue concerns the prediction of the resultant height of plastically deformed capping layers of silicon after cooling. A model which gives a lower and an upper bound on the height, based on an analytical spherical shell membrane stress equation, has been developed