Comparison of the catalytic activity of PHB–depolymerase,yeast lipase,and papain on poly(ethylene adipate), poly(ethylene succinate), and poly (3-hydroxybutyric acid)-co-(3-hydroxyvaleric acid)

PHB-depolymerase degraded poly[(3-hydroxybutyric acid)-co-(3-hydroxyvaleric acid)] (PHB/V) significantly. No other enzyme used in this study showed activity toward PHB/V. Weight loss and gel permeation chromatography (GPC) studies suggested that enzymatic degradation takes place by a surface erosion mechanism. pH studies demonstrated that enzymatic degradation occurs even when little weight loss is observed. Differential scanning calorimetry (DSC) analysis demonstrated that the enzymes studied prefer to degrade amorphous regions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2581–2585, 1999     

Parsimonious Optimization of Multitask Neural Network Hyperparameters

Neural networks are rapidly gaining popularity in chemical modeling and Quantitative Structure–Activity Relationship (QSAR) thanks to their ability to handle multitask problems. However, outcomes of neural networks depend on the tuning of several hyperparameters, whose small variations can often strongly affect their performance. Hence, optimization is a fundamental step in training neural networks although, in many cases, it can be very expensive from a computational point of view. In this study, we compared four of the most widely used approaches for tuning hyperparameters, namely, grid search, random search, tree-structured Parzen estimator, and genetic algorithms on three multitask QSAR datasets. We mainly focused on parsimonious optimization and thus not only on the performance of neural networks, but also the computational time that was taken into account. Furthermore, since the optimization approaches do not directly provide information about the influence of hyperparameters, we applied experimental design strategies to determine their effects on the neural network performance. We found that genetic algorithms, tree-structured Parzen estimator, and random search require on average 0.08% of the hours required by grid search; in addition, tree-structured Parzen estimator and genetic algorithms provide better results than random search.     

Analysis of Accelerometer and GPS Data for Cattle Behaviour Identification and Anomalous Events Detection

In this paper, a method to classify behavioural patterns of cattle on farms is presented. Animals were equipped with low-cost 3-D accelerometers and GPS sensors, embedded in a commercial device attached to the neck. Accelerometer signals were sampled at 10 Hz, and data from each axis was independently processed to extract 108 features in the time and frequency domains. A total of 238 activity patterns, corresponding to four different classes (grazing, ruminating, laying and steady standing), with duration ranging from few seconds to several minutes, were recorded on video and matched to accelerometer raw data to train a random forest machine learning classifier. GPS location was sampled every 5 min, to reduce battery consumption, and analysed via the k-medoids unsupervised machine learning algorithm to track location and spatial scatter of herds. Results indicate good accuracy for classification from accelerometer records, with best accuracy (0.93) for grazing. The complementary application of both methods to monitor activities of interest, such as sustainable pasture consumption in small and mid-size farms, and to detect anomalous events is also explored. Results encourage replicating the experiment in other farms, to consolidate the proposed strategy.     

A conformational role for NifW in the maturation of molybdenum nitrogenase P-cluster

Reduction of dinitrogen by molybdenum nitrogenase relies on complex metalloclusters: the [8Fe:7S] P-cluster and the [7Fe:9S:Mo:C:homocitrate] FeMo-cofactor. Although both clusters bear topological similarities and require the reductive fusion of [4Fe:4S] sub-clusters to achieve their respective assemblies, P-clusters are assembled directly on the NifD₂K₂ polypeptide prior to the insertion of FeMo-co, which is fully assembled separately from NifD₂K₂. P-cluster maturation involves the iron protein NifH₂ as well as several accessory proteins, whose role has not been elucidated. In the present work, two NifD₂K₂ species bearing immature P-clusters were isolated from an Azotobacter vinelandii strain in which the genes encoding NifH and the accessory protein NifZ were deleted, and characterized by X-ray absorption spectroscopy and EPR. These analyses showed that both NifD₂K₂ complexes harbor clusters that are electronically and structurally similar, with each NifDK unit containing two [4Fe:4S]^2+/+ clusters. Binding of the accessory protein NifW parallels a decrease in the distance between these clusters, as well as a subtle change in their coordination. These results support a conformational role for NifW in P-cluster biosynthesis, bringing the two [4Fe:4S] precursors closer prior to their fusion, which may be crucial in challenging cellular contexts.

Upon binding of NifW, a subtle conformation change occurs in NifD₂K₂, decreasing the distance between the two [4Fe:4S] clusters precursors of the P-cluster in nitrogenase.     

New Copoly(bisphenol-A)carbonates,Having Hydrophilic Porphyrin Units as End-Groups,Synthesized by Melt-Reacting Processes

The synthesis of some poly(bisphenol-A)carbonates (PCs) containing hydrophilic porphyrin units as end groups, by thermal treatment of commercial PC and 5,10,15-tri{p[ω-methoxy-poly(oxyethylene)]phenyl}20(p-hydroxy phenyl)porphyrin (I) blends, is reported. A suitable choice of reaction temperature, molar composition and reaction time, allowing the extent of the outer-inner transesterification reactions, leads to a gradual insertion of porphyrin units in the polymer chains. The composition of the obtained materials was inferred by GPC and MALDI-TOF mass spectrometric analysis.     

On the best approximation matrix problem for integrable matrix functions

In this paper positive definite matrix functionals defined on a set of square integrable matrix valued functions are introduced and studied. The best approximation problem is solved in terms of matrix Fourier series. Riemann-Lebesgue matrix property and a Bessel-Parseval matrix inequality are given.     

Identification of pyrolysis products of polysulphides by collisionally activated decomposition linked scanning mass spectrometry

Collisionally activated decomposition (CAD) linked scan mass spectra have been used in the identification of pyrolysis products obtained by the direct pyrolysis of some polysulphides in a mass spectrometer. Structures were determined by comparing the CAD spectra of the pyrolysis products with those of authentic compounds. The results are of help in elucidating the thermal degradation mechanisms that occur in the pyrolysis of the polysulphides investigated.     

Finding GM-estimators with global optimization techniques

In this note we address the problem of finding the GM-estimator for the location parameter of a univariate random variable. When this problem is non-convex but d.c. one can use a standard covering method, which, in the one-dimensional case has a simple form. In this paper we exploit the structure of the problem in order to obtain d.c. decompositions with certain optimality properties in the application of the algorithm. Numerical results show that this general-purpose algorithm outperforms previous ad-hoc methods for this problem.     

Numerical Solutions of Matrix Differential Models Using Higher-Order Matrix Splines

This paper deals with the construction of approximate solution of first-order matrix linear differential equations using higher-order matrix splines. An estimation of the approximation error, an algorithm for its implementation and some illustrative examples are included.     

On commutators of Wick products on CCR and CAR algebras

In this paper we study the q-commutator of Wick products on the CCR (canonical commutation relation) algebra and on the CAR (canonical anticommutation relation) algebra. We obtain a formula on q-commutator of Wick products in terms of Wick products of monomials of lower order. Moreover, we give a relation of double q-commutator.