Decompositions of metastable [C6H12O]+ ions with the oxygen on the third carbon: Ring-size preferences in [CnH2nO]+˙ ions

The isomerizations preceding the metastable decompositions in the mass spectrometer of a number of [C₆H₁₂O]⁺˙ ions with the oxygen on the third carbon are characterized utilizing deuterium labeling. Hydrogens are transferred in these ions by three-, five- and six-membered ring rearrangements, with propensities determined by features of the individual reactions. Three-membered ring hydrogen transfers between α and β-carbons are preferred to all five-membered ring hydrogen transfers. However, six-membered ring hydrogen transfers take place to the apparent exclusion of three-membered ring hydrogen transfers to enol carbons when the products are of comparable stability. The low-energy [C₆H₁₂O]⁺˙ isomerizations characterized are predictable from the behavior of their lower homologs. It is concluded that the determinants of these reactions are the same as those of other highly reactive organic intermediates.     

Linear Independence of Gabor Systems in Finite Dimensional Vector Spaces

We discuss the linear independence of systems ofmvectors in n-dimensional complex vector spaces where the m vectors are time-frequency shifts of one generating vector. Such systems are called Gabor systems. When n is prime, we show that there exists an open, dense subset with full-measure of such generating vectors with the property that any subset of n vectors in the corresponding full Gabor system of n² vectors is linearly independent. We derive consequences relevant to coding, operator identification and time-frequency analysis in general.     

Poly(methyl methacrylate) copolymers containing pendant carbazole and oxadiazole moieties for applications in single‐layer organic light emitting devices

Methyl methacrylate derived monomers functionalized with pendant carbazole and oxadiazole moieties were synthesized and could be copolymerized to form a random copolymer. The glass transition temperature of the copolymers could be predicted with a Fox equation and ranged from 140 to 191 °C. The photoluminescent characteristics of the copolymers, both in solution and in solid films, exhibited emission that was a combination of sharp and broad peaks, suggestive of monomeric and chromophore aggregation emission. These trends were also apparent in the electroluminescent response of the copolymers, where the appearance of an electromer emission was evident and was tentatively assigned to the carbazole moieties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7882–7897, 2008     

Vinylferrocene homopolymer and copolymers: an electrochemical comparison.

Poly(vinylferrocene) (pVFc) homopolymer was synthesized by free radical polymerization, along with a series of pVFc-based copolymers containing either styrene, vinylanthracene or methylmethacrylate. This report details the electrochemical experiments conducted to examine the stability of the various pVFc based polymers, which is shown to be critically dependent on the extent of copolymerization. A trend was found that when the concentration of co-monomer was decreased, electrochemical stability was enhanced. Furthermore incorporation of a second monomer into the polymer chain produced a profound effect on the scan rate behaviour of the vinylferrocene moiety. As the concentration of co-monomer was decreased, the behaviour tended towards that of a diffusion controlled process. These results are of vital significance for the development of pVFc-based electrochemical sensors.     

A Reader's Guide to Gacs's “Positive Rates” Paper

Peter Gacs's monograph, which follows this article, provides a counterexample to the important Positive Rates Conjecture. This conjecture, which arose in the late 1960's, was based on very plausible arguments, some of which come from statistical mechanics. During the long gestation period of the Gacs example, there has been a great deal of skepticism about the validity of his work. The construction and verification of Gacs's counterexample are unavoidably complex, and as a consequence, his paper is quite lengthy. But because of the novelty of the techniques and the significance of the result, his work deserves to become widely known. This reader's guide is intended both as a cheap substitute for reading the whole thing, as well as a warm-up for those who want to plumb its depths.     

High performance set associative translation lookaside buffers for low power microprocessors

A fast low power four-way set-associative translation lookaside buffer (TLB) is proposed. The proposed TLB allows single clock phase accesses at clock frequencies above 1 GHz. Comparisons to a conventional fully associative CAM tagged TLB, which is the type most commonly used in embedded processors, with the same number of entries on a 65 nm low standby power process show that the proposed design has 28% lower delay and up to 50% lower energy delay product. Unlike previous set-associative TLBs, which replicate the TLB to support multiple page sizes, multiple page sizes are supported on a way-by-way basis. Alternative conventional CAM tagged and set-associative TLBs are investigated with regard to access latency, power dissipation and hit rates.     

Scheduling networks of queues: Heavy traffic analysis of a simple open network

We consider a queueing network with two single-server stations and two types of customers. Customers of type A require service only at station 1 and customers of type B require service first at station 1 and then at station 2. Each server has a different general service time distribution, and each customer type has a different general interarrival time distribution. The problem is to find a dynamic sequencing policy at station 1 that minimizes the long-run average expected number of customers in the system.The scheduling problem is approximated by a dynamic control problem involving Brownian motion. A reformulation of this control problem is solved, and the solution is interpreted in terms of the queueing system in order to obtain an effective sequencing policy. Also, a pathwise lower bound (for any sequencing policy) is obtained for the total number of customers in the network. We show via simulation that the relative difference between the performance of the proposed policy and the pathwise lower bound becomes small as the load on the network is increased toward the heavy traffic limit.     

Constant amplitude and variable load history fatigue test results and predictions for cruciform and lap welds

Cruciform and lap welds were fatigue tested under constant amplitude axial load and SAE Bracket spectrum load conditions. For the cruciform joints, fatigue cracks generally initiate at the root but may initiate at the toe if higher bending stresses are induced by joint distortion. For lap welds, the stress ratio ($\text{R}$) and weld shape are the major factors influencing the fatigue crack initiation site.The fatigue test results were compared with predictions made using an analytical model developed by the authors, and good agreement between experiment and theory was observed. The model for the predictions assumes that the fatigue crack initiation period, which is the number of cycles for the initiation of a fatigue crack and its early growth and coalescence into a dominant fatigue crack, is the main portion of the total fatigue life at long lives.