Quality on Time

How is it that a group of talented, highly motivated, hard working software engineers consistently produce low-quality software, late? It is the author's view that schedule management and quality management go hand in hand. This paper discusses the notion that schedules are probability distributions, and presents several practical quality and schedule management techniques.     

Approximately optimal trees for group key management with batch updates

We investigate the group key management problem for broadcasting applications. Previous work showed that, in handling key updates, batch rekeying can be more cost effective than individual rekeying. One model for batch rekeying is to assume that every user has probability p$p$ of being replaced by a new user during a batch period with the total number of users unchanged. Under this model, it was recently shown that an optimal key tree can be constructed in linear time when p$p$ is a constant and in O(n⁴)$O\left(n^4\right)$ time when p→0$p\to 0$. In this paper, we investigate more efficient algorithms for the case p→0$p\to 0$, i.e., when membership changes are sparse. We design an O(n)$O\left(n\right)$ heuristic algorithm for the sparse case and show that it produces a nearly 2-approximation to the optimal key tree. Simulation results show that its performance is even better in practice. We also design a refined heuristic algorithm and show that it achieves an approximation ratio of 1+?$1+?$ for any fixed ?>0$?>0$ and n$n$, as p→0$p\to 0$. Finally, we give another approximation algorithm for any p∈(0,0.693)$p\in (0,0.693)$ which is shown to be quite good by our simulations.     

On the Parameterized Complexity of Layered Graph Drawing

We consider graph drawings in which vertices are assigned to layers and edges are drawn as straight line-segments between vertices on adjacent layers. We prove that graphs admitting crossing-free h-layer drawings (for fixed h) have bounded pathwidth. We then use a path decomposition as the basis for a linear-time algorithm to decide if a graph has a crossing-free h-layer drawing (for fixed h). This algorithm is extended to solve related problems, including allowing at most k crossings, or removing at most r edges to leave a crossing-free drawing (for fixed k or r). If the number of crossings or deleted edges is a non-fixed parameter then these problems are NP-complete. For each setting, we can also permit downward drawings of directed graphs and drawings in which edges may span multiple layers, in which case either the total span or the maximum span of edges can be minimized. In contrast to the Sugiyama method for layered graph drawing, our algorithms do not assume a preassignment of the vertices to layers. Research initiated at the International Workshop on Fixed Parameter Tractability in Graph Drawing, Bellairs Research Institute of McGill University, Holetown, Barbados, Feb. 9–16, 2001, organized by S. Whitesides. Research of Canada-based authors is supported by NSERC; research of Quebec-based authors is also supported by a grant from FCAR. Research of D.R. Wood completed while visiting McGill University. Research of G. Liotta supported by CNR and MURST.     

Characterization of His-X3-His sites in {alpha}-helices of synthetic metal-binding bovine somatotropin

Variants of bovine somatotropin have been engineered to containsynthetic metal-binding sites consisting of two solvent-exposedhistidines separated by a single turn of an -helix (His-X₃-Hisvariants). The affinities of these proteins for Cu(II) werecharacterized by measuring their partitioning coefficients inan aqueous two-phase polymer system. The partition coefficientswere used to generate binding constants for formation of a complexbetween the engineered metal-binding site and Cu(II) chelatedto an iminodiacetic acid derivative of polyethylene glycol.For three His-X₃-His variants described here, these constantsrange from 2x104 to 1.6x106 M-1. The metal affinity of a His-X₃-Hissite depends on the rigidity of the helix into which the siteis engineered. The affinities of the His-X₃-His sites for Cu(II)are large enough to dramatically increase not only the partitioningof these proteins in aqueous two-phase systems, but also theirretention times on a metal-affinity chromatography column. Boththese features can greatly facilitate the purification of engineeredproteins. Criteria for choosing positions for incorporatingmetal-binding sites are discussed.     

The Parameterized Complexity of Stabbing Rectangles

The NP-complete geometric covering problem Rectangle Stabbing is defined as follows: Given a set R of axis-parallel rectangles in the plane, a set L of horizontal and vertical lines in the plane, and a positive integer k, select at most k of the lines such that every rectangle is intersected by at least one of the selected lines. While it is known that the problem can be approximated in polynomial time within a factor of two, its parameterized complexity with respect to the parameter k was open so far. Giving two fixed-parameter reductions, one from the W[1]-complete problem Multicolored Clique and one to the W[1]-complete problem Short Turing Machine Acceptance, we prove that Rectangle Stabbing is W[1]-complete with respect to the parameter k, which in particular means that there is no hope for an algorithm running in f(k)?|R∪L| ^O(1) time. Our reductions also show the W[1]-completeness of the more general problem Set Cover on instances that “almost have the consecutive-ones property”, that is, on instances whose matrix representation has at most two blocks of 1s per row. We also show that the special case of Rectangle Stabbing where all rectangles are squares of the same size is W[1]-hard. The case where the input consists of non-overlapping rectangles was open for some time and has recently been shown to be fixed-parameter tractable (Heggernes et al., Fixed-parameter algorithms for cochromatic number and disjoint rectangle stabbing, 2009). By giving an algorithm running in (2k) ^k ?|R∪L| ^O(1) time, we show that Rectangle Stabbing is fixed-parameter tractable in the still NP-hard case where both these restrictions apply, that is, in the case of disjoint squares of the same size. This algorithm is faster than the one in Heggernes et al. (Fixed-parameter algorithms for cochromatic number and disjoint rectangle stabbing, 2009) for the disjoint rectangles case. Moreover, we show fixed-parameter tractability for the restrictions where the rectangles have bounded width or height or where each horizontal line intersects only a bounded number of rectangles.     

Enhanced thermal stability of high yttria concentration YSZ aerogels

Aerogels are a promising class of materials for lightweight, high-performance insulation. However, their high specific surface area contributes to rapid densification of the structure at elevated temperatures. Upon densification, the favorable properties of low thermal conductivity and low density are lost. Investigation of doped metal oxide systems presents a route to stabilization of porous structures at high temperatures and a platform to study parameters conducive to thermal stability. Our work focuses on yttria-stabilized zirconia (YSZ) aerogels prepared via a sol-gel method and supercritically dried. Yttria concentrations were studied from 0 to 50 mol% YO_1.5 to stabilize porosity to temperatures of 1200°C and develop an understanding of properties contributing to improved stability. Increased yttria content improved the thermal stability of the pore structure by reducing densification and suppressing crystallite growth, resulting in retention of the mesoporous structure to 1200°C. The improvement in thermal stability is related to associated reductions in specific surface energy and cation diffusivity at higher yttria concentrations. This work demonstrates that tuning thermodynamic and kinetic factors is a viable route to improved thermal stability in highly porous structures for use as insulation in extreme environments.     

Variation in the Drinking Trajectories of Freshmen College Students.

F. K. Del Boca, J. Darkes, P. E. Greenbaum, and M. S. Goldman (2004) examined temporal variations in drinking during the freshmen college year and the relationship of several risk factors to these variations. Here, using the same data, the authors investigate whether a single growth curve adequately characterizes the variability in individual drinking trajectories. Latent growth mixture modeling identified 5 drinking trajectory classes: light-stable, light-stable plus high holiday, medium-increasing, highdecreasing, and heavy-stable. In multivariate predictor analyses, gender (i.e., more women) and lower alcohol expectancies distinguished the light-stable class from other trajectories; only expectancies differentiated the high-decreasing from the heavy-stable and medium-increasing classes. These findings allow for improved identification of individuals at risk for developing problematic trajectories and for development of interventions tailored to specific drinker classes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Law-abiding and integrity on the Internet: A case for agents

Software agents extend the current, information-based Internet to include autonomous mobile processing. In most countries such processes, i.e., software agents are, however, without an explicit legal status. Many of the legal implications of their actions (e.g., gathering information, negotiating terms, performing transactions) are not well understood. One important characteristic of mobile software agents is that they roam the Internet: they often run on agent platforms of others. There often is no pre-existing relation between the “owner” of a running agent’s process and the owner of the agent platform on which an agent process runs. When conflicts arise, the position of the agent platform administrator is not clear: is he or she allowed to slow down the process or possibly remove it from the system? Can the interests of the user of the agent be protected? This article explores legal and technical perspectives in protecting the integrity and availability of software agents and agent platforms.     

Responses of Cereals to Residual Fertiliser Nitrogen Applied to the Preceding Potato Crop

The effects of N fertiliser and poultry manure, applied to potato crops, on soil mineral N (SMN) after harvest and on the grain N offtake (N_off) and yield of subsequent unfertilised cereal crops, were measured at six sites in England during 1989–1994. At three sites of medium textured soil N_off increased by between 0 and 49 kg ha^-1 and grain yield by between 0 and 2·1 t ha^-1, with increasing potato fertiliser N (PFN). The increases were greatest at applications of fertiliser N in excess of the optimum requirement for potatoes. No responses were found on two sandy and one shallow soil. Poultry manure applied in autumn or spring before the potatoes were planted increased N_off by between 0 and 52 kg ha^-1 and yield by between 0 and 2·1 t ha^-1 at one site on medium textured soil but not on one of the two sandy soils. These results suggest that, at the rates of fertiliser N currently recommended for potatoes, the N requirement of subsequent cereal crops may be reduced by between 20 and 40 kg ha^-1 on retentive soils but not on sandy and shallow soils. These reductions are less than currently recommended. However, the results also suggest that adjusting cereal fertiliser N according only to previous crop is unsatisfactory. The range of fertiliser N applied to potato crops in commercial practice is sufficiently great to significantly affect N_off, yield and hence the fertiliser N requirement of the subsequent cereal crop. © 1997 SCI.