Frequency and focal region properties of random sparse arrays

The concept of a random array relay, in terms of a sparse array, is introduced. The basic idea is to replace the relatively compact radiating structures encountered in conventional communication systems with widely and randomly dispersed radiating systems. The frequency and focal region properties of such random sparse arrays are treated. A methodology for obtaining the expected frequency response, focal region contours and depth of field for any random sparse array is given. The technique is exemplified with results for spherical and spherical-shell arrays. In addition, computer simulation results for sample functions of frequency responses and focal region contours are presented, both to verify the theoretical results and to illustrate some of the salient properties of random sparse arrays.     

Coset networks as connectors in parallel processors

An active area of research regarding parallel computer systems deals with the design of interconnection networks. Among all interconnection networks, permutation networks play a special role as all other networks can be constructed using such networks. It was recently shown that many permutation networks reported in the literature are manifestations of coset decompositions of symmetric groups. This result is generalized here to obtain several other previously unknown permutation networks which satisfy such decompositions. In addition, analyses of the edge-count, propagation delay, fan-out, and setup time of such networks are provided. The results lead to some anomolous behavior as well as several trade-offs among these parameters. For example, it is shown that a complete bipartite graph is the fastest and most economical direct realization of a permutation network. Furthermore, it is shown that the fan-out of a network is inversely proportional to the propagation delay whereas the setup time may or may not relate to the propagation delay at all depending on the network in question. Finally, two constant fan-out implementations of these networks using O (n ^1.59) 2 × 1 multiplexers and 2 × 2 switches are presented.This work is supported in part by the National Science Foundation under Grant No: CCR-8708864.     

Metal-Containing Polymers Synthesized via Acyclic Diene Metathesis (ADMET) Polymerization Using Electrochemically Reduced Tungsten-Based Catalyst: Polycarbogermanes

Various germanium-containing dienes, bis(4-pentenyl)diethylgermanium (1), bis(4-pentenyl)dimethylgermanium (2) and bis(3-butenyl)diethylgermanium (3), were synthesized and polymerized using an electrochemically reduced tungsten-based catalyst system via acyclic diene metathesis (ADMET) polymerization. All polymer structures were characterized by ¹H- and ¹³C-NMR spectroscopy. These results indicate the retention of the double bonds in the polymer structure with high trans content (57–70%) as expected from a step condensation reaction. These polymers have low molecular weight (M _W) that range from 7400 to 19,100. The thermal stability of polymers was evaluated by thermogravimetric analysis. The glass transition temperatures of the polymer of monomer 1, 2 and 3 were −24, −9 and −47°C, respectively. Synthesis, characterization and the general limitations of ADMET polymers obtained by this catalyst are discussed. An erratum to this article can be found at     

Mineralogy-induced radiological aspects with characterization of commercial granites exploited in Turkey

This study deals with natural radioactivity levels of the ten most important commercial granites from various districts currently being exploited as dimension stone in Turkey. Determining the level of radioactivity is important for human health, particularly for indoor use of granites. This study shows that the relationship between the natural radioactivity and the radiogenic mineralogical contents of the granites exploited for commercial utilization in Turkey is variable. The natural radioactivity levels (i.e., activity concentrations of radionuclides ²²⁶Ra, ²³²Th, and ⁴⁰K) of granite samples were determined by high-resolution gamma-ray spectrometry. Using these activities, radiological hazard dose rates (absorbed and annual effective) and gamma-activity indexes were calculated using standard equations accepted by public health bodies, taking relevant international reports and guidelines into account. Three of the granites exploited in the Black Sea, Aegean, and Central Anatolia regions were found to be high in radium-equivalent activities and annual effective doses due to minerals bearing the radionuclides, including zircon, apatite, allanite, xenotime, uranothorite, K-feldspars, and biotite. Of those, uranothorite contains large amounts of radionuclides and is present in samples of granites collected from the Black Sea and Aegean regions. Radioactivity measurements using high-resolution gamma-ray spectroscopy serve as a rapid screening tool to evaluate natural radioactivity, whereas detailed petrographic, mineralogical, and elemental investigations can reveal the source of radioactive emissions in granites.     

Electrodeposition of poly(4‐methyl carbazole‐3‐carboxylic acid) on steel surfaces and corrosion protection of steel

The electropolymerization of 4‐methyl carbazole‐3‐carboxylic acid was successfully performed on a stainless steel (316L) surface with lithium perchlorate/acetonitrile as the supporting electrolyte. The corrosion resistance of the new coating, poly(4‐methyl carbazole‐3‐carboxylic acid) (PCz), was investigated. To this end, potentiodynamic polarization curves, open circuit potentials, and electrochemical impedance spectroscopy were used to evaluate the capacity of the PCz coating to protect the steel surface. The corrosion tests indicated that PCz exhibited effective anodic protection in a corrosive test solution. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A simulation-based comparison of two goods-to-person order picking systems in an online retail setting

Design and analysis of order picking systems continues to be an active topic of interest both in academia and practice, especially in light of the significant increase in online retail sales. In this paper, we examine two types of well-known, goods-to-person order picking systems, namely, a miniload system and a Kiva system. Using a simulation model, we compare the performance of the two systems on the basis of expected throughput and expected container retrieval times to process the same set of customer orders. We also discuss some of the advantages and limitations of the two systems.     

Expected move request waiting times in single-device, polling-based material handling systems

We present an analytical approach to approximate the expected waiting times of move requests (customers) served by a single handling device (server) that operates according to the First-Encountered-First-Served (FEFS) rule, which is a common rule employed for polling-based material handling systems. Under the FEFS rule, the device inspects each station according to a prespecified polling sequence and serves the first move request it encounters. Polling resumes as soon as the device completes serving a move request. The expected waiting times are important for estimating the expected Work-In-Process (WIP) levels at individual stations and to gauge the overall performance of the system. Moreover, the polling sequence itself can affect the expected waiting times. If the device meets the throughput requirement under more than one polling sequence, the results we present can also be used to evaluate alternative polling sequences. In fact, using the analytical results and a numerical example, we show that alternative polling sequences, even if they impose the same “workload factor” on the device, can lead to significantly different expected WIP levels