Decellularized Human Skeletal Muscle as Biologic Scaffold for Reconstructive Surgery

Engineered skeletal muscle tissues have been proposed as potential solutions for volumetric muscle losses, and biologic scaffolds have been obtained by decellularization of animal skeletal muscles. The aim of the present work was to analyse the characteristics of a biologic scaffold obtained by decellularization of human skeletal muscles (also through comparison with rats and rabbits) and to evaluate its integration capability in a rabbit model with an abdominal wall defect. Rat, rabbit and human muscle samples were alternatively decellularized with two protocols: n.1, involving sodium deoxycholate and DNase I; n.2, trypsin-EDTA and Triton X-NH₄OH. Protocol 2 proved more effective, removing all cellular material and maintaining the three-dimensional networks of collagen and elastic fibers. Ultrastructural analyses with transmission and scanning electron microscopy confirmed the preservation of collagen, elastic fibres, glycosaminoglycans and proteoglycans. Implantation of human scaffolds in rabbits gave good results in terms of integration, although recellularization by muscle cells was not completely achieved. In conclusion, human skeletal muscles may be effectively decellularized to obtain scaffolds preserving the architecture of the extracellular matrix and showing mechanical properties suitable for implantation/integration. Further analyses will be necessary to verify the suitability of these scaffolds for in vitro recolonization by autologous cells before in vivo implantation.     

In vitro digestion rate and resistant starch content of tortillas stored at two different temperatures

In vitro indicators of starch bioavailability were evaluated in freshly prepared maize tortillas and compared to those exhibited by 24, 48 or 72 h-stored samples. Storage took place either at room temperature (approx. 25 °C) or under refrigeration (4 °C). Potentially available starch (AS) content decreased from 670 g kg⁻¹ in the control tortilla to 583 g kg⁻¹ in 72 h-stored preparations. Concomitant increases in total resistant starch (RS) and retrograded resistant starch (RRS) were recorded upon storage. RRS content in 72 h-stored samples (35-39 g kg⁻¹) doubled that of freshly prepared tortillas. Changes in AS, RS and RRS were not affected by storage temperature. Both initial rate and final point of starch hydrolysis by pancreatic amylase were reduced in samples kept for 48 and 72 h, without influence of storage temperature. Storage length is suggested as a major determinant of the bioavailability of starch in tortillas.     

Precession electron diffraction‐assisted crystal phase mapping of metastable c‐GaN films grown on (001) GaAs

The control growth of the cubic meta‐stable nitride phase is a challenge because of the crystalline nature of the nitrides to grow in the hexagonal phase, and accurately identifying the phases and crystal orientations in local areas of the nitride semiconductor films is important for device applications. In this study, we obtained phase and orientation maps of a metastable cubic GaN thin film using precession electron diffraction (PED) under scanning mode with a point‐to‐point 1 nm probe size beam. The phase maps revealed a cubic GaN thin film with hexagonal GaN inclusions of columnar shape. The orientation maps showed that the inclusions have nucleation sites at the cubic GaN {111} facets. Different growth orientations of the inclusions were observed due to the possibility of the hexagonal {0001} plane to grow on any different {111} cubic facet. However, the generation of the hexagonal GaN inclusions is not always due to a 60° rotation of a {111} plane. These findings show the advantage of using PED along with phase and orientation mapping, and the analysis can be extended to differently composed semiconductor thin films. Microsc. Res. Tech. 77:980–985, 2014. © 2014 Wiley Periodicals, Inc.     

Comments on: “Gallium-doped ZnO thin films deposited by chemical spray”: [Sol. Energy Mater. Sol. Cells 87 (2005) 107–116]

In this communication, I will discuss some aspects concerning a paper recently published by H. Gomez et al. on the properties of gallium-doped ZnO thin films deposited by chemical spray methods [H. Gomez, A. Maldonado, M. de la L. Olvera, D.R. Acosta, Sol. Energy Mater. Sol. Cells 87 (2005) 107.]. I believe that there are some wrong considerations of basic principles, some incorrect experimental procedures and inconsistencies on the analysis and throughout the paper. The “Introduction” reflects some knowledge on the subject, but it seems that the authors of the aforementioned paper use outdated background sources in some cases, and inconsistently apply prior research in others.The “Experimental procedure” shows some serious lack of knowledge concerning thin films that are potentially applicable as transparent electrodes in photovoltaic devices. In the “Results and discussion”, I found some of the arguments and statements contradictory, mainly when the effects of their vacuum annealing were being discussed. Considerations on the “Structural properties” are necessary, as they are not appropriate for comparative purposes. Finally, a last point, but not less important than the others, is the “Conclusions” of the paper. Some suggestions are made below for the improvement of this, and several others, aspects of the paper.     

Nonlinear analysis of tilted toroidal thermosyphon models

We analyze one-dimensional models for single-phase tilted toroidal thermosyphons for three different heating conditions: known heat flux, known wall temperature and mixed heating. For the first two the governing equations lend themselves to exact reduction to a set of three ordinary differential equations, while for the third the equations remain coupled as an infinite set. For all three cases, the tilt angle is stabilizing while the heat rate is a destabilizer. A nonlinear analysis is carried out using center manifold theory and normal form analysis. The known heat flux solutions lose stability through a supercritical Hopf bifurcation, while for the other two heating conditions the Hopf bifurcation is supercritical under some conditions and subcritical under others. Stable limit-cycle oscillations exist only for the supercritical cases, otherwise instability leads directly to chaos. Analysis also provides an estimate for the amplitude of oscillation for the supercritical conditions. Numerical experiments have confirmed the theoretical predictions qualitatively and quantitatively.     

Enhancement of indirect sulphation of limestone by steam addition

The effect of water (H?O(g)) on in situ SO? capture using limestone injection under (FBC) conditions was studied using a thermobalance and tube furnace. The indirect sulphation reaction was found to be greatly enhanced in the presence of H?O(g). Stoichiometric conversion of samples occurred when sulphated with a synthetic flue gas containing 15% H?O(g) in under 10 h, which is equivalent to a 45% increase in conversion as compared to sulphation without H?O(g). Using gas pycnometry and nitrogen adsorption methods, it was shown that limestone samples sulphated in the presence of H?O(g) undergo increased particle densification without any significant changes to pore area or volume. The microstructural changes and observed increase in conversion were attributed to enhanced solid-state diffusion in CaO/CaSO? in the presence of H?O(g). Given steam has been shown to have such a strong influence on sulphation, whereas it had been previously regarded as inert, may prompt a revisiting of the classically accepted sulphation models and phenomena. These findings also suggest that steam injection may be used to enhance sulfur capture performance in fluidized beds firing low-moisture fuels such as petroleum coke.     

Selective assembling of calixarenes and pseudorotaxanes on Si(100) and polycrystalline copper

We report the first compared study of the anchoring mode of calix[6]arene derivatives and pseudorotaxanes on Si(100) and polycrystalline Cu. Calixarenes have been chosen for their flexibility as linkers, being, i.a., efficient building blocks for the constructing of molecular devices based on pseudorotaxanes and rotaxanes. A covalent functionalization on Si or Cu surfaces requires the molecules to be differently modified: thiol (-SH) or C double bond C terminations are respectively suitable for Cu or H-Si(100). Anchoring on Cu was reached by dipping a clean substrate in a calix[6]arene-SH solution, while a wet-chemistry recipe was followed for Si(100), combined with an extra-mild photochemical activation via visible light. Molecular adhesion onto either surfaces has been demonstrated by the presence of XPS signals from specific elements in the molecules: calix[6]arene designed for H-Si were derivatized with NO2 groups on the upper rim of the calix, while the S atom was used as the molecular identifier on Cu. A further extension is represented by the anchoring reaction of rotaxanes on Si(100) and Cu surfaces. A pseudorotaxane species was first formed in solution by reacting a calix[6]arene "wheel," bearing three N-phenylureido groups on the upper rim, with viologen (4,4'-bipyridinium) containing axle. The resulting species has then been anchored on either Cu and Si via its distinct termination of the axle. This two-step reaction has produced a threaded pseudorotaxane covalently bound to either surfaces, as shown by XPS results. These species are ready to respond to external stimuli. We also cross-checked the two different anchoring groups for their reactivity on Cu and Si surfaces. No molecular uptake was observed when two solutions, containing calixarenes with the anchoring arms intended either for Si or Cu surfaces, were exchanged.     

Study of validity of the single-diode model for solar cells by I–V curves parameters extraction using a simple numerical method

The I–V measurement of solar cells is one of the most employed electrical characterization techniques in the photovoltaics research field due to the valuable information one can obtain from such a curve. Parameters like Voc, Isc and the maximum power can be easily observed at a glance. Furthermore, additional information can be extracted by a more exhaustive analysis involving the equivalent electrical circuit of a solar cell which is based on ideal electrical components with a well-defined behavior. This equivalent circuit is typically assumed to be formed by a current source in parallel with a single diode and a shunt resistor, connected to a series resistor. However, this model does not take into account the separate contributions of the different carrier transport mechanisms in solar cells; for example, carrier diffusion and recombination-generation in the depletion region. Therefore, the single diode model may not be suitable in many practical cases. In this work, a simple numerical method was developed to extract the parameters for both single diode and double diode models from experimental I–V curves of solar cells. The developed numerical algorithm was applied to extract the parameters for a published benchmark solar cell which has been used for testing this kind of algorithms. The extracted parameters using our simple method are comparable with other more sophisticated and computer power demanding algorithms. Thereafter, we applied the developed algorithm to extract the single-diode parameters from simulated “experimental” I–V curves, where two carrier transport mechanisms are present, trying to understand under what conditions the single diode approximation would provide meaningful parameters for such experimental curves. It is shown that the extracted parameters can vary strongly, particularly for the dark saturation current and ideality factor, without much variation of the root mean square error between the experimental data and the model, causing these values to be unreliable and its physical interpretation misleading. We show that the same algorithm can be applied to a double diode (two exponentials) model providing physically meaningful parameters without much computing power requirements. In summary, there is no further justification for using a single diode model to interpret the experimental I–V curves of real solar cells.     

Probabilistic assessment of the safety profile of the Fischer–Tropsch process with a supercritical solvent

Inherent safety assessment during the design stage of chemical processes is typically conducted based on average values for design parameters. Under those conditions, the single-point deterministic process performance assessment may be affected by the phenomenon known as the ‘flaw of averages’ in the presence of irreducible sources of uncertainty (performance evaluated at average conditions does not represent average performance). In this work, an inherent process safety assessment developed under a probabilistic formulation is presented. An evaluation of the proposed approach is performed in the case of a gas-to-liquid process system using a supercritical solvent for Fischer–Tropsch reactor systems. The pertinent uncertainty analysis is carried out using Monte Carlo simulation techniques to account for the propagation of uncertainty through the inherent process safety model and the derivation of probability distribution profiles for the associated metrics, thus statistically characterizing ranges of potential performance outcomes. The response variables were the autothermal reactor and the syngas flows. The results show that the input variables associated to the autothermal flow potentially generate the most hazardous conditions for the process. The results also show how the metrics are affected when uncertainty is explicitly taken into account at the design stage of the process, offering a more nuanced assessment and characterization of the inherent process safety profile.     

The impact of reading fluency level on interactive information retrieval

Given an information need and the corresponding set of documents retrieved, it is known that user assessments for such documents differ from one user to another. One frequent reason that is put forward is the discordance between text complexity and user reading fluency. We explore this relationship from three different dimensions: quantitative features, subjective-assessed difficulty, and reader/text factors. In order to evaluate quantitative features, we wondered whether it is possible to find differences between documents that are evaluated by the user and those that are ignored according to the complexity of the document. Secondly, a task related to the evaluation of the relevance of short texts is proposed. For this end, users evaluated the relevance of these short texts by answering 20 queries. Documents complexity and relevance assessments were done previously by some human experts. Then, the relationship between participants assessments, experts assessments and document complexity is studied. Finally, a third experimentation was performed under the prism of neuro-Information Retrieval: while the participants were monitored with an electroencephalogram (EEG) headset, we tried to find a correlation among EEG signal, text difficulty and the level of comprehension of texts being read during the EEG recording. In light of the results obtained, we found some weak evidence showing that users responded to queries according to text complexity and user’s reading fluency. For the second and third group of experiments, we administered a sub-test from the Woodcock Reading Mastery Test to ensure that participants had a roughly average reading fluency. Nevertheless, we think that additional variables should be studied in the future in order to achieve a sound explanation of the interaction between text complexity and user profile.