EQUIL: a program for the modeling of low-pressure differentiation processes in natural mafic magma bodies

The use of a two-lattice model for the activity of silicate melt components permits temperature dependent, compositionally independent distribution coefficients to be derived. The compositional independence of these functions allows a model to be constructed of phase equilibria applicable to a wide range of natural mafic systems. Using the phase equilibria model as a base, the program EQUIL was constructed. Given an initial primitive parental mafic composition, EQUIL enables one to model most low-pressure differentiation processes involving fractionation. These include magma chamber recharge, fractional or equilibria crystallization, assimilation and tapping of the magma chamber. Lines of descent can be calculated for a magma body undergoing a single differentiation process, or several processes together (i.e. paired assimilation and fractional crystallization).     

Biorationals fromNicotiana protect cucumbers againstColletotrichum lagenarium (Pass.) ell. & halst disease development

Trichome exudate compounds isolated from leaves ofNicotiana tabacum, N. glutinosa (accessions 24 and 24a), and 21 otherNicotiana species were evaluated for biorational activity againstC. lagenarium, the anthracnose pathogen of cucumber. Exudate compounds tested were the cembrane diterpenes - and -4,8,13-duvatriene-1,3-diols (DVT diols); the labdane diterpenes (13-E)-labda-13-ene-8,15-diol (labdenediol) and (13-R)-labda-14-ene-8, 13-diol (sclareol); extracts fromN. gossei; and various sugar ester isolates. In dose-response experiments test compounds were applied to a water agar surface that was then inoculated with a conidial suspension. Low levels of most test compounds reduced or completely inhibited germination ofC. lagenarium conidia. IC₅₀ values, concentrations (micrograms per square centimeter) at which conidium germination was reduced 50%, were 6.3 for DVT diols, 19.3 for sclareol, 1.0 for labdenediol, 2.8 for a mixture of sclareol and labdenediol, 1.2 for anN. gossei sucrose ester and 4.1 for theN. gossei crude extract. Higher levels of DVT diols and the sclareol-labdenediol mixture were required to reduce lesion size and number on inoculated cucumber leaves. At the highest concentration tested, 100 µg/cm², the DVT diols and sclareol-labdenediol mixtures protected cucumbers against lesion development by 93 and 98%, respectively. Sugar ester mixtures from 20Nicotiana species and three different sugar ester fractions fromN. bideglovii had in vitro antifungal activity at a concentration of 48 µg/cm². Sugar esters from nine of the species includingN. acuminata, N. attenuata, N. clevelandii, N. maritima, N. miersii, N. noctiflora, N. occidentalis, N. rustica, and fractions 10, 12, and 13 fromN. bideglovii completely inhibitedC. lagenarium conidium from germinating. Sugar ester mixtures from only four species,N. plumbaginifolia, N. bonariensis, N. simulans, andN. palmerii, had no significant effect onC. lagenarium conidium germination. These results suggest the potential ofNicotiana exudates as biorationals in reducing disease development.     

Preserving knowledge in software projects

Up-to-date preservation of project knowledge like developer communication and design documents is essential for the successful evolution of software systems. Ideally, all knowledge should be preserved, but since projects only have limited resources, and software systems continuously grow in scope and complexity, one needs to prioritize the subsystems and development periods for which knowledge preservation is more urgent. For example, core subsystems on which the majority of other subsystems build are obviously prime candidates for preservation, yet if these subsystems change continuously, picking a development period to start knowledge preservation and to maintain knowledge for over time become very hard. This paper exploits the time dependence between code changes to automatically determine for which subsystems and development periods of a software project knowledge preservation would be most valuable. A case study on two large open source projects (PostgreSQL and FreeBSD) shows that the most valuable subsystems to preserve knowledge for are large core subsystems. However, the majority of these subsystems (1) are continuously foundational, i.e., ideally for each development period knowledge should be preserved, and (2) experience substantial changes, i.e., preserving knowledge requires substantial effort.     

Spectral Mixture Analysis: Linear and Semi-parametric Full and Iterated Partial Unmixing in Multi- and Hyperspectral Image Data

As a supplement or an alternative to classification of hyperspectral image data linear and semi-parametric mixture models are considered in order to obtain estimates of abundance of each class or end-member in pixels with mixed membership. Full unmixing based on both ordinary least squares (OLS) and non-negative least squares (NNLS), and the partial unmixing methods orthogonal subspace projection (OSP), constrained energy minimization (CEM) and an eigenvalue formulation alternative are dealt with. The solution to the eigenvalue formulation alternative proves to be identical to the CEM solution. The matrix inversion involved in CEM can be avoided by working on (a subset of) orthogonally transformed data such as signal maximum autocorrelation factors, MAFs, or signal minimum noise fractions, MNFs. This will also cause the partial unmixing result to be independent of the noise isolated in the MAF/MNFs not included in the analysis. CEM and the eigenvalue formulation alternative enable us to perform partial unmixing when we know one desired end-member spectrum only and not the full set of end-member spectra. This is an advantage over full unmixing and OSP. The eigenvalue formulation of CEM inspires us to suggest an iterated CEM scheme. Also the target constrained interference minimized filter (TCIMF) is described. Spectral angle mapping (SAM) is briefly described. Finally, semi-parametric unmixing (SPU) based on a combined linear and additive model with a non-linear, smooth function to represent end-member spectra unaccounted for is introduced. An example with two generated bands shows that both full unmixing, the CEM, the iterated CEM and TCIMF methods perform well. A case study with a 30 bands subset of AVIRIS data shows the utility of full unmixing, SAM, CEM and iterated CEM to more realistic data. Iterated CEM seems to suppress noise better than CEM. A study with AVIRIS spectra generated from real spectra shows (1) that ordinary least squares in this case with one unknown spectrum performs better than non-negative least squares, and (2) that although not fully satisfactory the semi-parametric model gives better estimates of end-member abundances than the linear model.     

Alternative 2D Shape Representations using the Symmetry Set

Among the many attempts made to represent families of 2D shapes in a simpler way, the Medial Axis takes a prominent place. Its graphical representation is intuitively appealing and can be computed efficiently. Small perturbations of the shape can have large impact on the and are regarded as instabilities, although these changes are mathematically known from the investigations on a super set, the Symmetry Set . This set has mainly been in a mathematical research stage, partially due to computational aspects, and partially due to its unattractive representation in the plane. In this paper novel methods are introduced to overcome both aspects. As a result, it is possible to represent the as a string is presented. The advantage of such a structure is that it allows fast and simple query algorithms for comparisons. Second, alternative ways to visualize the are presented. They use the distances from the shape to the set as extra dimension as well as the so-called pre-Symmetry Set and anti-Symmetry Set. Information revealed by these representations can be used to calculate the linear string representation structure. Example shapes from a data base are shown and their data structures derived. Arjan Kuijper is Senior Researcher at the Johann Radon Institute (RICAM) of the Austrian Academy of Sciences in Linz, Austria. He received his M.Sc. degree in applied mathematics in 1995 from the University of Twente, The Netherlands. During the period 1996–1997 he worked at ELTRA Parkeergroep, Ede, The Netherlands. He has been a Ph.D. student (1997–2001), associate researcher (2001–2002), and postdoc (202) at the Institute of Information and Computing Sciences of Utrecht University. In 2003-2005 he served as assistant research professor at the IT University of Copenhagen in Denmark. His interest subtends all mathematical aspects of image and shape analysis, notably multi-scale representations (scale spaces), catastrophe and singularity theory, medial axes and symmetry sets, partial differential equations, singular theories, and their applications. Ole Fogh Olsen is associate professor in the image group at the IT University of Copenhagen. He received the PhD degree in 2000 in computer science from University of Copenhagen, Denmark. Main research interest areas are image analysis, medical image analysis and computer vision with focus on scale space theory, differential geometry, singularity theory, statistics, segmentation, optic flow and shape modelling. Peter Giblin is Professor of Mathematics at the University of Liverpool and a former Head of the Mathematical Sciences Department. He joined the staff there in 1967 and has been visiting professor at the University of North Carolina at Chapel Hill, Five Colleges in Amherst, Massachusetts, and Brown University. His research interests are in singularity theory and its applications to differential geometry and computer vision. Mads Nielsen received a MSc in 1992 and a PhD in 1995 both in computer science from DIKU, Department of Computer Science, University of Copenhagen, Denmark. During his PhD studies he spent one year 93–94 at the Robotvis lab at INRIA, Sophia-Antipolis, France. In the second half of 1995 he was post-doc at the Image Sciences Institute of Utrecht University, The Netherlands. In 1996 he was joint post-doc at DIKU and 3D-Lab, School of Dentistry, University of Copenhagen, where he served as assistant professor 1997–99. In 1998–99 he served as external associate professor at Institute of Mathematical Modelling, Technical University of Denmark. April 1999 he became the first associate professor at the new IT University of Copenhagen. Since June 2002 he has been professor the same place heading the Image Analysis Group. He is head of the PhD-studies at ITU, member of the Academical Council of ITU, General chair of MICCAI 2006, member of the editorial board of IJCV and JMIV. His research interests are in the mathematical foundation of image analysis, the computational aspects, and the applications, especially in the medical area.     

Coherent radiance capture of scenes under changing illumination conditions for relighting applications

Relighting algorithms make it possible to take a model of a real-world scene and virtually modify its lighting. Unlike other methods that require controlled conditions, we introduce a new radiance capture method that allows the user to capture parts of the scene under different lighting conditions. A novel calibration method is presented that finds the positions of reflective spheres and their mathematically accurate projection onto the scene geometry. The resulting radiance distribution is used to estimate a diffuse reflectance for each object, computed coherently using the appropriate light probe image. Finally, the scene is relit using a novel illumination pattern.     

Roles as a structuring tool in online discussion groups: The differential impact of different roles on social knowledge construction

This study focuses on stimulating social knowledge construction in e-discussions and examines the introduction of five roles: starter, summariser, moderator, theoretician, and source searcher. Asynchronous discussion groups of 10 1st-year students Instructional Sciences were organised to foster students’ processing of the learning content. Four successive authentic tasks of three weeks each were presented. Taking into account the moment of introduction of the role assignment (at the start of the discussions versus at the end), the differential impact of the roles on knowledge construction is studied through quantitative content analysis based on the interaction analysis model of Gunawardena, Lowe, and Anderson (1997). The results show a positive effect of role assignment on students’ social knowledge construction at the start of the discussions. This implies that roles should be introduced at the start of the discussions and can be faded out towards the end. With respect to the differential impact of the roles, the results show that messages from moderators, theoreticians, and summarisers reflect higher levels of knowledge construction at the start of the discussions. Even students without a role in role-supported groups benefit from the role introduction.