Modeling of sporicidal effect of hydrogen peroxide in the sterilization of low density polyethylene film inoculated with Bacillus subtilis spores

The sporicidal effect of hydrogen peroxide (H₂O₂) in the sterilization of low density polyethylene film (LDPE) was evaluated using a Central Composite Design (CCD). The effects of contact time (5-19s), bath temperature (23–70 °C) and concentration of H₂O₂ (0–35%) in an immersion bath were investigated. A 16 cm² film surface was evenly inoculated with 100 μL of the test microorganism Bacillus subtilis var. globigii ATCC9372 spores. The effective H₂O₂ sporicidal activity was demonstrated at concentrations from 18 to 35% and in a temperature range from 46 to 70 °C, resulting in 2–7 decimal reductions of B. subtilis spores. A quadratic mathematical model representative of the action of H₂O₂ on the B. subtilis spores was developed as a function of concentration, time and temperature. Test specimens sanitized with 28% H₂O₂ at 60 °C for 8 s showed 4 decimal reductions. In the same sterilization procedure, but extending the time to 16 s, this value increased to 7 decimal reductions, demonstrating the efficiency of H₂O₂ as a function of contact time. The sterilization system tested showed satisfactory performance in the sterilization of LDPE films, being capable of reaching up to 7 decimal reductions of the bacterial spore population.     

Low- to medium-temperature geothermal reserves in Mexico: a first assessment

In this work we make a first, partial, assessment of the low- to medium-temperature geothermal reserves of Mexico. The assessment covers about 30% of the identified geothermal surface manifestations. For reserve assessment we use the volume method, supplemented by Montecarlo simulations and statistics, in order to quantify the inherent uncertainties. We estimate these reserves as lying between 7.7 × 10¹⁶ and 8.6 × 10¹⁶ kJ, with 90% confidence. The distribution of most likely reservoir temperatures is in the 60–180 °C range, with a mean of 111 °C. These massive amounts of recoverable energy and the associated temperatures are potentially important for the economic development of the associated geothermal localities.     

Neural Networks as Inference and Learning Engines

Abstract: This paper presents an abridgment of a neural network constructive methodology and applications with real data. The neural network can be considered as the learning core and inference engine of an expert system that produces either different network designs or simulations as output, its input being data sequences. Basically, it consists of additive structural learning, limiting it by a cross-validation technique.
Considerations about uncertainty treatment in neural networks are also presented, including uncertainty in data, in neuron activation, in outputs, and combination of several uncertainty sources.
Applications include three different sets of data, all of them related to the energy field. First, river streamflow estimation is discussed. Then CO₂ concentration prediction from gas injection rate is studied. Finally, the program learns to imitate a feedwater control system in a nuclear reactor. All tests show good results, as can be seen when compared with other standard methods.     

Effects of Temperature and Concentration on the Rheological Behavior of Polyacrylamide-Based Polymers

Polymers are high molecular weight molecules that provide high viscosity at low concentrations to the media they are inserted. In the oil industry, they are used for enhanced oil recovery and for drilling fluids, where its viscosity is an important factor for a greater efficiency. From all the polymers used by industry, the polyacrylamide and the biopolymer xantham gum are those, which appear significantly in those applications. Taking that into consideration, this work intends to study the effects of the physical, chemical and structural parameters of those polymers in their rheological behaviour, by varying their concentrations from 400 ppm to 2,000 ppm and their temperatures from 298 K to 328 K, which are values similar to those found in the field. For that, a Brookfield Viscometer-Brookfield Engineering Labs rheometer was used. The results acquired showed that the increase on the polyacrylamides ionicity generates and increase on the medium viscosity. For the temperature, its increase causes a reduction of viscosity for the low ionicity polyacrylamides, while increases the viscosity for the high ionicity ones. In the comparative study between xantham gum and polyacrylamides, it was possible to notice that, even though the biopolymer is more complex, its viscosity still is lower when compared to the polyacrylamides.     

Field Properties in Surface Irrigation Management and Design

Field properties—topography, hydraulic resistance, and infiltration—play an important role in the performance of surface irrigation systems, and appropriate characterizations of these are required as data input to simulation or design software. The EWRI/ASCE Task Committee on Soil and Crop Hydraulic Properties has been charged with preparing a guide for practitioners faced with such data entry. The result is this special section of the Journal of Irrigation and Drainage Engineering in which this paper is the first in the series presented. It describes the characteristics of these field properties and notes a series of caveats to be considered when dealing with them in the course of analyses or designs of surface irrigation systems.     

Tests of Random Walk: A Comparison of Bootstrap Approaches

This paper compares different versions of the multiple variance ratio test based on bootstrap techniques for the construction of empirical distributions. It also analyzes the crucial issue of selecting optimal block sizes when block bootstrap procedures are used. The comparison of the different approaches using Monte Carlo simulations leads to the conclusion that methodologies using block bootstrap methods present better performance for the construction of empirical distributions of the variance ratio test. Moreover, the results are highly sensitive to methods employed to test the null hypothesis of random walk.     

Fly ash addition in clayey materials to improve the quality of solid bricks

The technical quality of two compositionally different groups of solid bricks fired between 800 and 1000 °C was evaluated. Five weight percentage of fly ash was added to both groups and they were compared with similar bricks with no added fly ash.The textures of the bricks with fly ash were very similar to the textures of those without it, except that the samples with the additive contained spherical fly ash particles with diameters ranging from 0.1 to 10 μm. These particles led to a reduction in the density of the bricks and a substantial improvement in their durability, with less decay being caused by salt crystallization in the pores. This is because fly ash causes a reduction in the number of micropores, the pores that make porous materials most vulnerable to salt-induced decay. Use of this additive could have practical implications as a means of recycling and for achieving cost savings in brick production.     

Effect of structural modifications in the laser properties of polymer films doped with perylenebisimide derivatives

In this work we study the effect of different types of modifications of the chemical structure of perylenebisimide derivatives (PBIs) in the laser properties of PBI-doped polystyrene films at various concentrations. In particular, we focus on controlling the wavelength of emission, in order to tune the laser wavelength, as well as on increasing the amount of PBI in the films, aiming to decrease the laser thresholds, while keeping a good photostability. Amplified spontaneous emission (ASE) was observed for all compounds, the best performance being obtained for films doped with PBIs symmetrically substituted at the imide positions, that emitted at 580 nm with a threshold of 20 kW/cm² and a photostability half-life of 30,000 pump pulses. Substitution at the bay positions of the PBI core and replacement of imide functions by anhydride groups allow to red-shift the emission wavelength up to 645 nm, but the thresholds increase considerably and the photostability is reduced. PBIs are among the most photostable materials reported in the literature and show very reasonable thresholds. In addition they have a great potential for their application in the field of data communications based on poly(methyl methacrylate) optical fibers, with low-loss transmission windows between 530 and 590 nm and at 650 nm.     

Architectural Control of Freeze-Cast Ceramics Through Additives and Templating

The freezing of concentrated colloidal suspensions is a complex physical process involving a large number of parameters. These parameters provide unique tools to manipulate the architecture of freeze-cast materials at multiple length scales in a single processing step. However, we are still far from developing predictive models to describe the growth of ice crystals in concentrated particle slurries. In order to exert reliable control over the microstructural formation of freeze-cast materials, it is necessary to reach a deeper understanding of the basic relationships between the experimental conditions and the microstructure of the growing solid. In this work, we explore the role of several processing variables (e.g., composition of the suspension, freezing rate, and patterning of the freezing surface) that could affect the formulation strategies for the architectural manipulation of freeze-cast materials. We also demonstrate, using freeze-cast lamellar structures, that reducing the lamellar thickness by less than half increases the compressive strength by more than one order of magnitude.