Biogenic Calcium Carbonate: Calcite Crystals of Variable Morphology by the Reaction of Aqueous Ca2+ Ions with Fungi

The biological synthesis of CaCO₃ crystals of variable morphology by challenging non‐calcareous microorganisms such as fungi with aqueous Ca²⁺ ions has been described. Many fungi are known to produce reasonable amounts of CO₂ during growth. We show here that CO₂ and characteristic proteins released from the fungi Fusarium oxysporum and Trichothecium sp. may be reacted with aqueous Ca²⁺ ions to produce truly biogenic CaCO₃ crystals. While calcite crystals are obtained with both fungi, significant differences in the morphology of the crystals is observed, indicating that the proteins secreted by the fungi play a crucial role in directing the morphology of the calcite crystals. The action of specific proteins secreted by the microorganisms in directing calcite crystal morphology as well as the more complex issue of synergistic action of mixtures of proteins in directing crystal structure and morphology has been addressed.     

An N-terminal fragment of the gene 4 helicase/primase of bacteriophage T7 retains primase activity in the absence of helicase activity

Primase and helicase activities of bacteriophage T7 are present in a single polypeptide coded by gene 4. Because the amino terminal region of the gene 4 protein contributes to primase activity, we constructed a truncated gene 4 encoding the N-terminal 271-aa residues. The truncated protein, purified from cells overexpressing the protein, is a dimer in solution; the full-length protein is a hexamer. Although the fragment is devoid of dTTPase and helicase activities, it catalyzes template-directed synthesis of di-, tri-, and tetranucleotides. The rates for tetraribonucleotide synthesis and for dinucleotide extension on a 20-nucleotide template are similar for the full-length and truncated proteins. However, the activity of the primase fragment is unaffected by dTTP whereas the primase activity of the full-length protein is stimulated >14-fold. The primase fragment is defective in the interaction with T7 DNA polymerase in that primer synthesis cannot be coupled to DNA synthesis.     

Molecular reconstruction and homology modelling of the catalytic domain of the common ancestor of the haemostatic vitamin-K-dependent serine proteinases

The vitamin-K-dependent serine proteinases of coagulation have evolved by a process of gene duplication and divergence, acquiring along the way a considerable degree of functional diversity that has equipped them for their different roles in haemostasis. The cDNA sequences encoding the catalytic domains of the early mammalian ancestors of five vitamin-K-dependent factors (factors VII, IX and X, protein C and prothrombin) were reconstructed by employing cDNA sequence data from a range of extant mammals and by using established phylogenies. The cDNA sequence of the putative common ancestor of these early mammalian proteins was then reconstructed from the five sequences by using a deduced phylogeny that was different in a number of respects from those previously proposed. Factor IX is proposed to have branched off early on, followed by protein C and prothrombin and finally factors VII and X. Significant differences in mutation rates were observed between proteins within a species; factor IX exhibited a lower mutation rate than the other proteins, consistent with its early emergence. Differences in mutation rates were also observed between species for a given protein and these exhibited an inverse correlation with generation time. A biophysically plausible structure for the ancestral vitamin-K-dependent factor protein was constructed by comparative methods. Studies of the functional architecture of this model provide new insights into the evolution of protein-binding specificity in this family of proteins.     

Development of Texture in Interstitial-Free Steel Processed by Equal-Channel Angular Pressing

Ti + Nb-stabilised interstitial-free steel is deformed by equal-channel angular pressing (ECAP) adopting a route B_C up to an equivalent strain of 24. Upon ECAP the grain size decreases to ultrafine level and it becomes strongly textured. At ε_vm = 0.6-6, components of both {110} fiber, \( J_{\uptheta } \), \( \bar{J}_{\uptheta } \) and of 〈111〉 fiber, D _1θ, D _2θ with common components of E _θ, \( \bar{E}_{\uptheta } \) are existing but after ε_vm ≥9, only 〈111〉 fiber components are observed. At large strain, ε_vm = 9-24, 〈111〉 fiber texture is recorded with monoclinic symmetry. At ε_vm = 0.6, coarse grains get split into deformation bands. Fragmentation of bands (at ε_vm = 3) suppress \( \bar{J}_{\uptheta } , \) \( J_{\uptheta } \) components. At ε_vm = 6, formation of lamellar structures increases intensity of mainly D _1θ, D _2θ. At ε_vm = 9, oriented ribbon grains result in strong D _1θ, D _2θ components with 〈111〉 fiber. At ε_vm = 15-24, conversion of ribbon grains to near-equiaxed shaped grains maintains 〈111〉 fiber texture with enhanced intensity of D _1θ and D _2θ components.     

Daily intake of heavy metals by infants through milk and milk products

Concentrations of the essential elements Zn and Cu and potentially toxic elements Pb and Cd in different milk samples and baby food materials were measured, primarily to assess whether the intakes comply with recommended desired levels for essential and permissible levels for toxic elements. The geometric mean concentrations of Pb, Cd, Cu and Zn in different types of milk were found to vary from 1.70 to 3.35, 0.07 to 0.10, 43.2 to 195 and 1772 to 4230 micrograms/l, while the same in different baby foods had values from 39.5 to 77.7, 0.45 to 17.7, 1106.3 to 3157.3 and 9367 to 34,592 micrograms/kg, respectively. The concentration of Cd was found to be very low (0.1 microgram/l) and fairly constant in all types of milk. The lead content in cow milk was observed to be lowest even in comparison with breast milk. Concentrations of all these metals are approximately one order of magnitude higher in baby food products than those observed in different types of milk owing to higher fat content. The infant baby food Amul Spray contains low concentrations of toxic (Pb and Cd) and high concentrations of essential (Cu and Zn) elements. The daily intakes of Pb, Cd, Cu and Zn by infants through milk and baby foods marketed in Mumbai city have also been estimated. The daily intakes of Pb (1.1 micrograms/kg) and Cd (0.01 microgram/kg) for infants through baby foods are well below the recommended tolerable levels of 3.57 micrograms/kg and 0.8-1.0 microgram/kg, respectively. Similarly the daily intake levels of essential elements are also significantly lower than the recommended desirable levels of 3-5 mg and 0.5-1.0 mg for Zn and Cu, respectively. Milk from an Indian mother also does not provide adequate levels of essential elements to the infants and children.     

Mathematical Modeling and Microbiological Verification of Ohmic Heating of a Multicomponent Mixture of Particles in a Continuous Flow Ohmic Heater System with Electric Field Parallel to Flow

To accomplish continuous flow ohmic heating of a low‐acid food product, sufficient heat treatment needs to be delivered to the slowest‐heating particle at the outlet of the holding section. This research was aimed at developing mathematical models for sterilization of a multicomponent food in a pilot‐scale ohmic heater with electric‐field‐oriented parallel to the flow and validating microbial inactivation by inoculated particle methods. The model involved 2 sets of simulations, one for determination of fluid temperatures, and a second for evaluating the worst‐case scenario. A residence time distribution study was conducted using radio frequency identification methodology to determine the residence time of the fastest‐moving particle from a sample of at least 300 particles. Thermal verification of the mathematical model showed good agreement between calculated and experimental fluid temperatures (P > 0.05) at heater and holding tube exits, with a maximum error of 0.6 °C. To achieve a specified target lethal effect at the cold spot of the slowest‐heating particle, the length of holding tube required was predicted to be 22 m for a 139.6 °C process temperature with volumetric flow rate of 1.0 × 10^?4 m³/s and 0.05 m in diameter. To verify the model, a microbiological validation test was conducted using at least 299 chicken‐alginate particles inoculated with Clostridium sporogenes spores per run. The inoculated pack study indicated the absence of viable microorganisms at the target treatment and its presence for a subtarget treatment, thereby verifying model predictions.     

Singularity-free dynamic equations of vehicle–manipulator systems

In this paper we derive the singularity-free dynamic equations of vehicle–manipulator systems using a minimal representation. These systems are normally modeled using Euler angles, which leads to singularities, or Euler parameters, which is not a minimal representation and thus not suited for Lagrange’s equations. We circumvent these issues by introducing quasi-coordinates which allows us to derive the dynamics using minimal and globally valid non-Euclidean configuration coordinates. This is a great advantage as the configuration space of the vehicle in general is non-Euclidean. We thus obtain a computationally efficient and singularity-free formulation of the dynamic equations with the same complexity as the conventional Lagrangian approach. The closed form formulation makes the proposed approach well suited for system analysis and model-based control. This paper focuses on the dynamic properties of vehicle–manipulator systems and we present the explicit matrices needed for implementation together with several mathematical relations that can be used to speed up the algorithms. We also show how to calculate the inertia and Coriolis matrices and present these for several different vehicle–manipulator systems in such a way that this can be implemented for simulation and control purposes without extensive knowledge of the mathematical background. By presenting the explicit equations needed for implementation, the approach presented becomes more accessible and should reach a wider audience, including engineers and programmers.