Validation of scientific topic models using graph analysis and corpus metadata

Probabilistic topic modeling algorithms like Latent Dirichlet Allocation (LDA) have become powerful tools for the analysis of large collections of documents (such as papers, projects, or funding applications) in science, technology an innovation (STI) policy design and monitoring. However, selecting an appropriate and stable topic model for a specific application (by adjusting the hyperparameters of the algorithm) is not a trivial problem. Common validation metrics like coherence or perplexity, which are focused on the quality of topics, are not a good fit in applications where the quality of the document similarity relations inferred from the topic model is especially relevant. Relying on graph analysis techniques, the aim of our work is to state a new methodology for the selection of hyperparameters which is specifically oriented to optimize the similarity metrics emanating from the topic model. In order to do this, we propose two graph metrics: the first measures the variability of the similarity graphs that result from different runs of the algorithm for a fixed value of the hyperparameters, while the second metric measures the alignment between the graph derived from the LDA model and another obtained using metadata available for the corresponding corpus. Through experiments on various corpora related to STI, it is shown that the proposed metrics provide relevant indicators to select the number of topics and build persistent topic models that are consistent with the metadata. Their use, which can be extended to other topic models beyond LDA, could facilitate the systematic adoption of this kind of techniques in STI policy analysis and design.

     

Technological and sensorial properties of liquid nitrogen ice cream enriched with protein from brewing waste (trub)

Debittered trub (brewing waste) is an important source of protein source (70.26%). Trub and whey protein were used for 5% protein enrichment of ice cream frozen by liquid nitrogen. Three formulations were elaborated: ice cream standard (ICS), ice cream with whey protein (ICW) and ice cream with trub (ICT). Chemical composition, rheological properties, texture, overrun, melting rate, scanning electron microscopy and a sensorial test were performed. Results showed that ICT presented a higher viscosity, obtained on the upward curve up to 6.76 Pa s⁻¹, consistency index (22.96 (Pa s⁻¹)ⁿ), hysteresis area (140.40 mPa s⁻¹) and hardness (31113.33 g) but a lower melting rate (0.38 g min⁻¹), overrun (13.92%) and sensorial acceptability than the other formulations. The addition of trub debittered for protein enrichment improved ice cream properties and demonstrated that it could be used as a food ingredient.     

Kinetic,thermodynamic parameters and in vitro digestion of tannase from Aspergillus tamarii URM 7115

Tannase is an enzyme used in various industries and produced by a large number of microorganisms. The aim of this study was to evaluate tannase production to determine the biochemical, kinetic, and thermodynamic properties and to simulate tannase in vitro digestion. The tannase-producing fungal strain was isolated from “jamun” leaves and identified as Aspergillus tamarii. Temperature at 26°C for 67?h was the best combination for maximum tannase activity (6.35-fold; initial activity in Plackett–Burman design—15.53?U/mL and average final activity in Doehlert design—98.68?U/mL). The crude extract of tannase was optimally active at 40°C, pH 5.5 and 6.5. Moreover, tannase was stimulated by Na⁺, Ca²⁺, Mg²⁺, and Mn²⁺. The half-life at 40°C lasted 247.55?min. The free energy of Gibbs, enthalpy, and entropy, at 40°C, was 81.47, 16.85, and ?0.21?kJ/mol?·?K, respectively. After total digestion, 123.95% of the original activity was retained. Results suggested that tannase from A. tamarii URM 7115 is an enzyme of interest for industrial applications, such as gallic acid production, additive for feed industry, and for beverage manufacturing, due to its catalytic and thermodynamic properties.     

The Effect of Ozone Gas-Liquid Contacting Conditions in a Static Mixer on Microorganism Reduction

The effect of gas-liquid contacting conditions in a static mixer on ozone transfer efficiency and reduction of Bacillus subtilis spores was studied in an experimental ozone contactor. An empirical mathematical model was developed that related the transfer efficiency in the experimental system to the superficial liquid velocity in the mixer, the gas-liquid flow rate ratio and the height of the down-stream bubble column. Spore reduction was determined primarily by the dissolved ozone concentration-time (C_avgt_m) product in the reactive flow segment and was independent of the gas-liquid contacting conditions in the static mixer. In an integrated ozone contacting system, the static mixer should be designed to maximize ozone mass transfer while the reactive flow segment should be designed for efficient microorganism reduction.     

Physicochemical Properties of Palm Oil-Based Puff Pastry Model Margarines Related to Their Baking Performance in Long-Term Storage

Developing trans-free alternative fat solutions suitable for specific applications remains a challenge in edible fats and other domains. This is particularly true for palm oil-based puff pastry margarines, which suffer from post crystallization problems, leading to dramatic loss of functionality. This research is aimed at investigating the influence of triacylglycerol (TAG) compositions of palm oil-based puff pastry margarines on the physical properties of the fat crystal network, which determine the functionality of such products. Three model puff pastry margarines are produced at pilot scale under the same crystallization conditions. They share the same fatty acid composition and close solid fat content (SFC) profiles, whereas the proportions of major TAG (tripalmitoylglycerol (PPP), 1,3-di-palmitoyl-2-oleoylglycerol (POP), 1,2-di-palmitoyl-3-oleoylglycerol (PPO), 1,2-dioleoyl-3-palmitoylglycerol (POO)) are different. Polymorphism, melting profile, hardness, microscopic structures, and baking performance (puffing effect) of the model fats are examined during a period of 6 months. The following results are obtained: 1) The TAG composition significantly influences the post crystallization processes occurring in palm oil-based margarines. 2) High amounts of POP show negative influences. 3) The proportions of POP, PPO, and PPP should be carefully balanced to prevent detrimental crystal network rearrangements, leading to textural modifications (hardness increase) and significant reduction in baking performance. Practical Applications : The results presented in this work could be helpful for edible fat products developers, especially for roll-in fat applications. This research provides an overview of the relevant properties to study for the assessment of puff pastry margarine functionality. It also highlights the importance of ensuring long-term stability of palm oil-based fat products. Finally, it emphasizes that certain combinations of fat materials should be avoided to maintain the quality of palm oil-based puff pastry margarines.     

A new variety of low-linolenic rapeseed oil; Characteristics and room-odor tests

Two Canadian rapeseed oils, “Westar” and “low-linolenic”, supplied by the Canola Council were studied and compared with a French rapeseed. The linolenic acid content of the low-linolenic variety is about 3%. This drop in the C18∶3 is completely compensated for by an increase in the C18∶2. Seventy-two percent of the triglycerides with at least one linolenic chain disappeared. A strong increase in the OOL and OLL was observed. The room-odor tests showed that the “low-linolenic” had a significantly higher odor score than the French rapeseed and the “Westar”, both of these being very similar. A fruity odor dominated in the “low-linolenic”, and the fishy painty odors were particularly reduced.     

Electrooxidation of CO and CO/H2 mixtures on a Pt-Sn catalyst prepared by an implantation method

A new type of ion implantation technique is used to create a non-equilibrium Pt-Sn(IMP) near-surface alloy with ca. 8.6 at% Sn. The surface composition was determined by low-energy ion-scattering (LEIS). The kinetics of the electrooxidation of CO and 2% CO/H₂ mixtures on Pt-Sn(IMP) is essentially identical to that of Pt₃Sn(110). The fact that any non-equilibrium composition can be easily prepared by this implantation method opens an interesting practical opportunity to create a new Pt-Sn alloy fuel cell catalyst having an otherwise unobtainable surface composition of Sn. This method also appears to have general utility in alloy catalysis as a means of exploring compositions in thermodynamically unfavorable regions of the bulk phase diagram. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sparse Non-negative Stencils for Anisotropic Diffusion

We introduce a new discretization scheme for Anisotropic Diffusion, AD-LBR, on two and three dimensional Cartesian grids. The main features of this scheme is that it is non-negative and has sparse stencils, of cardinality bounded by 6 in 2D, by 12 in 3D, despite allowing diffusion tensors of arbitrary anisotropy. The radius of these stencils is not a-priori bounded however, and can be quite large for pronounced anisotropies. Our scheme also has good spectral properties, which permits larger time steps and avoids e.g. chessboard artifacts. AD-LBR relies on Lattice Basis Reduction, a tool from discrete mathematics which has recently shown its relevance for the discretization on grids of strongly anisotropic Partial Differential Equations (Mirebeau in Preprint, 2012). We prove that AD-LBR is in 2D asymptotically equivalent to a finite element discretization on an anisotropic Delaunay triangulation, a procedure more involved and computationally expensive. Our scheme thus benefits from the theoretical guarantees of this procedure, for a fraction of its cost. Numerical experiments in 2D and 3D illustrate our results.