Atom‐transfer radical polymerization of methyl methacrylate (MMA) using CuSCN as the catalyst

The effect of CuSCN as a catalyst in atom‐transfer radical polymerization (ATRP) was investigated. CuSCN can successfully be used for the ATRP of MMA. Substituted bipyridines as well as imines can be used to stabilize the copper complex in solution. CuSCN induces faster polymerization compared to CuBr and CuCl when tosylchloride is used as the initiator. However, the polydispersity is larger than that obtained in the cases of CuCl and CuBr.     

A note on comparing response times in the M/GI/1/FB and M/GI/1/PS queues

We compare the overall mean response time (a.k.a. sojourn time) of the processor sharing (PS) and feedback (FB) queues under an M/GI/1 system. We show that FB outperforms PS under service distributions having decreasing failure rates; whereas PS outperforms FB under service distributions having increasing failure rates.     

Mass spectrometry of poly(methyl methacrylate) (PMMA) prepared by atom transfer radical polymerization (ATRP)

Poly(methyl methacrylate) (PMMA) was synthesized via atom transfer radical polymerization (ATRP). As a catalyst copper(I)thiocyanate (CuSCN) was used with N-n-pentyl-2-pyridylmethanimine as a ligand. Infrared spectroscopy and matrix assisted laser desorption ionization time-of-flight mass spectrometry were used to characterize the synthesized polymers. From this it was clear that at least to some extent thiocyanate was present as end groups of the PMMA chains. This observation is discussed in view of a phenomenon called halogen exchange, which has been reported before for bromine/chlorine exchange in ATRP.     

An elementary proof of the restricted invertibility theorem

We give an elementary proof of a generalization of Bourgain and Tzafriri’s Restricted Invertibility Theorem, which says roughly that any matrix with columns of unit length and bounded operator norm has a large coordinate subspace on which it is well-invertible. Our proof gives the tightest known form of this result, is constructive, and provides a deterministic polynomial time algorithm for finding the desired subspace.     

Semidefinite optimization in discrepancy theory

Recently, there have been several new developments in discrepancy theory based on connections to semidefinite programming. This connection has been useful in several ways. It gives efficient polynomial time algorithms for several problems for which only non-constructive results were previously known. It also leads to several new structural results in discrepancy itself, such as tightness of the so-called determinant lower bound, improved bounds on the discrepancy of the union of set systems and so on. We will give a brief survey of these results, focussing on the main ideas and the techniques involved.