A strong-coupling expansion for fermion field theories and the large-N limit of the gross-neveu model

An expansion in the fermion propagator is formulated for the N-species Gross-Neveu model in the large-N limit. Different regularisation schemes may be adopted and we compare two. We find that a continuum momentum cut-off is easiest to work with and automatically avoids spurious fermionic states which afflict a naive lattice formulation. Chiral symmetry is broken at zeroth order and the resulting expansion is inverse powers of g²N simplifies considerably for large N. In this limit the strong-coupling expansion may be summed to all orders. Extrapolation techniques, like Padé approximants, are not needed. Using a momentum cut-off we recover all the exact results previously derived by summing weak-coupling expansions.     

Physical vapor deposition method for the high-throughput synthesis of solid-state material libraries

A method that combines co-evaporation of pure elements from multiple finite-size sources on temperature-controlled substrates with independently controlled source shutters has been used for the synthesis of solid-state material combinatorial libraries. The source shutters are positioned to achieve a controlled gradient of the deposited elements across the substrate and are fixed during the course of deposition. Choice of the shutter position and the rate of deposition for each source allow the direct synthesis of continuous and controlled materials of varying composition. There are significant advantages of the method over alternatives which rely on sequential deposition and subsequent heat treatment to produce thin film materials. The parameters governing the creation of gradients have been identified and defined. Simulations and experimental data have been compared in the case of a single source. Results are presented for the synthesis of a ternary alloy library to demonstrate the methodology.     

Three takes on telecom's troubles

Spectrum asked three IEEE members from the telecommunications sector to comment on the industry's current woes and prospects. Roch Guerin discusses bandwidth as a commodity and how to deal with it. The impact of technological change on telecommunications is enormous and calls for a shift in business models. Technology is making bandwidth a commodity and it should not matter who supplies it. Competition is vital and commodity providers must be decoupled from value providers. Frank Ferrante points out that the Year 2000 crisis resulted in manufacturers being deluged with orders for new upgraded systems. Vast sums were spent to meet the demand in time. However, when Y2K was over, production stayed high and inventories continued to build, while demand effectively stopped overnight. Dazzling new innovations are needed to compel the masses to spend and manufacturers must apply their resources to deliver quickly and efficiently. Jules A. Bellisio discusses the role of engineers in bringing new ideas to the market place. Many engineers have put together ventures for the sole purpose of attracting capital. The underlying technology and business propositions were there solely to lure the unsuspecting. By allowing engineers to use technology simply to cover for a scam, then the profession is also to blame for the current problems.     

On protective buffer policies

Studies buffering policies which provide different loss priorities to packets/cells, while preserving packet ordering (space priority disciplines). These policies are motivated by the possible presence, within the same connection, of packets with different loss probability requirements or guarantees, e.g., voice and video coders or rate control mechanisms. The main contribution of the paper is the identification and evaluation of buffering policies which preserve packet ordering and guarantee high priority packets performance (loss probability), irrespective of the traffic intensity and arrival patterns of low priority packets. Such policies are termed protective policies. The need for such policies arises from the difficulty to accurately characterize and size low priority traffic, which can generate large and unpredictable traffic variations over short periods of time. The authors review previously proposed buffer admission policies and determine if they satisfy such “protection” requirements. Furthermore, they also identify and design new policies, which for a given level of protection maximize low priority throughput     

On equivalent definitions of the correlation dimension for a probability measure

In mathematical physics, one sometimes has to deal with averages of the type $$M\mu (T) = \frac{1}{{T^n }}\int\limits_{|\xi | \leqslant T} { d\xi |\hat \mu (\xi )|^2 , T > 0}$$ where $\hat \mu$ is the Fourier transform of some probability Borel measure μ. We show that the asymptotic behavior ofMμ is governed by the usual (upper and lower) correlation dimension of the measure μ.     

Novel biodegradable copolyesters containing blocks of poly(3-hydroxyoctanoate) and poly(epsilon-caprolactone): synthesis and characterization

Novel biodegradable polyester block copolymers have been synthesized by using well-defined poly(3-hydroxyoctanoate) (PHO) oligomers having a hydroxyl end group and an ester end group with M(n) values of 800, 2,500, 5,300, 8,000, or 20,000 as an elastomeric soft segment and poly(epsilon-caprolactone) as a more crystalline segment. These PHO oligomers prepared by methanolysis were subjected to block copolymerization with epsilon-caprolactone. The chemical structure of the copolymers was confirmed by (1)H NMR and (13)C NMR spectroscopy. All the copolyesters are semi-crystalline and two T(g) were observed by differential scanning calorimetry when the molecular weight of the PHO block is about 20,000.     

Amine-catalyzed addition of azide ion to alpha,beta-unsaturated carbonyl compounds

[formula: see text] A new protocol for the beta-azidation of alpha,beta-unsaturated carbonyl compounds is described. The method employs tertiary amines as catalysts for azide addition. The azide source is a 1:1 mixture of TMSN3 and AcOH. Tertiary amines, either in solution or bound to a solid support, are efficient catalysts for the reaction.