Lipid and myoglobin oxidation in pork stored in oxygen- and carbon dioxide-enriched atmospheres

The formation of malonaldehyde and metmyoglobin in pork muscles stored in oxygen- and carbon dioxide-enriched atmospheres at 1°C was followed. The formation of metmyoglobin at the surface of the muscles was independent of carbon dioxide concentration. However, increased oxygen concentration caused a significant decrease in the rate of metmyoglobin formation; the surface concentration of metmyoglobin was below 30% even after 15 days' storage in 80% oxygen/20% carbon dioxide. Lipid oxidation, as measured by malonaldehyde production (TBA Number), occurred at the same rate in air an mixtures containing 80, 90 and 100% oxygen. In some muscles, the rate was such that rancidity was apparent within 6 days at 1°C and, for pork, lipid oxidation, and not bacterial spoilage or metmyyoglobin formation, may be the limiting factor in the use of oxygen-containing atmospheres for storage.     

N‐Arylsulfonyl Indolines as Retinoic Acid Receptor‐Related Orphan Receptor γ (RORγ) Agonists

The nuclear retinoic acid receptor‐related orphan receptor γ (RORγ; NR1F3) is a key regulator of inflammatory gene programs involved in T helper 17 (T_H17) cell proliferation. As such, synthetic small‐molecule repressors (inverse agonists) targeting RORγ have been extensively studied for their potential as therapeutic agents for various autoimmune diseases. Alternatively, enhancing T_H17 cell proliferation through activation (agonism) of RORγ may boost an immune response, thereby offering a potentially new approach in cancer immunotherapy. Herein we describe the development of N‐arylsulfonyl indolines as RORγ agonists. Structure–activity studies reveal a critical linker region in these molecules as the major determinant for agonism. Hydrogen/deuterium exchange coupled to mass spectrometry (HDX‐MS) analysis of RORγ–ligand complexes help rationalize the observed results.     

Integrating K-means clustering with a relational DBMS using SQL

Integrating data mining algorithms with a relational DBMS is an important problem for database programmers. We introduce three SQL implementations of the popular K-means clustering algorithm to integrate it with a relational DBMS: 1) a straightforward translation of K-means computations into SQL, 2) an optimized version based on improved data organization, efficient indexing, sufficient statistics, and rewritten queries, and 3) an incremental version that uses the optimized version as a building block with fast convergence and automated reseeding. We experimentally show the proposed K-means implementations work correctly and can cluster large data sets. We identify which K-means computations are more critical for performance. The optimized and incremental K-means implementations exhibit linear scalability. We compare K-means implementations in SQL and C++ with respect to speed and scalability and we also study the time to export data sets outside of the DBMS. Experiments show that SQL overhead is significant for small data sets, but relatively low for large data sets, whereas export times become a bottleneck for C++.     

Efficiently repairing and measuring replica consistency in distributed databases

In a distributed database, maintaining large table replicas with frequent asynchronous insertions is a challenging problem that requires carefully managing a tradeoff between consistency and availability. With that motivation in mind, we propose efficient algorithms to repair and measure replica consistency. Specifically, we adapt, extend and optimize distributed set reconciliation algorithms to efficiently compute the symmetric difference between replicated tables in a distributed relational database. Our novel algorithms enable fast synchronization of replicas being updated with small sets of new records, measuring obsolence of replicas having many insertions and deciding when to update a replica, as each table replica is being continuously updated in an asynchronous manner. We first present an algorithm to repair and measure distributed consistency on a large table continuously updated with new records at several sites when the number of insertions is small. We then present a complementary algorithm that enables fast synchronization of a summarization table based on foreign keys when the number of insertions is large, but happening on a few foreign key values. From a distributed systems perspective, in the first algorithm the large table with data is reconciled, whereas in the second case, its summarization table is reconciled. Both distributed database algorithms have linear communication complexity and cubic time complexity in the size of the symmetric difference between the respective table replicas they work on. That is, they are effective when the network speed is smaller than CPU speed at each site. A performance experimental evaluation with synthetic and real databases shows our algorithms are faster than a previous state-of-the art algorithm as well as more efficient than transferring complete tables, assuming large replicated tables and sporadic asynchronous insertions.     

Composite electrode modelling and optimization for solid oxide fuel cells

In a solid oxide fuel cell (SOFC), the electrode is a composite porous structure, which can be considered to be made of ionic conductor material, electronic conductor material and pores that function as channels for the flow of reacting gases. This article proposes a model for the composite electrode of an SOFC, suitable for optimization. The model can be used to study the effects on fuel cell performance of pore diameter, porosity and tortuosity, electrical conductivity, ionic conductivity, electrode temperature, inlet reacting gas pressure, diffusivity and activation energy for the reaction. The article illustrates the use of the proposed model to find an optimal thickness of the active reaction layer by the minimization of total potential losses, or alternatively by the maximization of the fuel cell net power output. A three‐way single SOFC optimization was conducted with respect to the active reaction layer thicknesses at both electrodes, operating temperature and electrode porosity, showing that the SOFC net power density varies approximately by factor of 2, which stresses the importance of the developed model for SOFC design and optimization. This work provides a way to incorporate aspects of the electrode composition and microstructure in the evaluation of the fuel cell performance. For the ranges of electrode active reaction layer thicknesses studied in this article, the variation of net power density reached 16% at T = 973 K and 11% at T = 1173 K in the two‐way optimization. Regarding porosity, in the three‐way optimization, the net power density variation reached 10% at T = 1073 K. Therefore, the cumulative effects in the three‐way optimization for a fixed temperature show that net power density can vary approximately by 20%. Copyright © 2012 John Wiley & Sons, Ltd.     

Thermodynamic optimization of a solar system for cogeneration of water heating and absorption cooling

This paper presents a contribution to understanding the behavior of solar‐powered air conditioning and refrigeration systems with a view to determining the manner in which refrigeration rate, mass flows, heat transfer areas, and internal architecture are related. A cogeneration system consisting of a solar concentrator, a cavity‐type receiver, a gas burner, and a thermal storage reservoir is devised to simultaneously produce heat (hot water) and cooling (absorption refrigerator system). A simplified mathematical model, which combines fundamental and empirical correlations, and principles of classical thermodynamics, mass and heat transfer, is developed. The proposed model is then utilized to simulate numerically the system transient and steady‐state response under different operating and design conditions. A system global optimization for maximum performance (or minimum exergy destruction) in the search for minimum pull‐down and pull‐up times, and maximum system second law efficiency is performed with low computational time. Appropriate dimensionless groups are identified and the results are presented in normalized charts for general application. The numerical results show that the three‐way maximized system second law efficiency, η_{II,max,max,max}, occurs when three system characteristic mass flow rates are optimally selected in general terms as dimensionless heat capacity rates, i.e. (ψ_ss, ψ_wxwx, ψ_Hs)_opt=(0.335, 0.28, 0.2). The minimum pull‐down and pull‐up times, and maximum second law efficiencies found with respect to the optimized operating parameters are sharp and, therefore, important to be considered in actual design. As a result, the model is expected to be a useful tool for simulation, design, and optimization of solar energy systems in the context of distributed power generation. Copyright © 2008 John Wiley & Sons, Ltd.     

The Hardware-based PKCS#11 Standard using the RSA Algorithm

In this paper, we have proposed and implemented a hardware-based security system, which executes RSA-based cryptography operations by using the PKCS#11 standard. It was implemented in C, VHDL and FPGAs and it is modular and easily adaptable to the future upgrades for the communication among machines and devices. Any cryptography algorithm can be used; however, in our project we only used the RSA as a case study. We did simulations and real tests that allowed verifying the correct behavior and execution of our project; we used the RSA with keys up to 512 bits. Real tests showed the transmission of ciphered data between our project (PKCS#11 and RSA) and a PC by using serial communication.     

A volume element model (VEM) for energy systems engineering

This work presents a simplified modeling and simulation approach for energy systems engineering that is capable of providing quick and accurate responses during system design. For that, the laws of conservation are combined with available empirical and theoretical correlations to quantify the diverse types of flows that cross the system and produce a simplified tridimensional mathematical model, namely a volume element model (VEM). The physical domain of interest is discretized in space, thus producing a system of algebraic and ODEs with respect to time, whose solution delivers the project variables spatial distribution and dynamic response. In order to illustrate the application of the VEM in energy systems engineering, three example problems are considered: (i) a regenerative heat exchanger; (ii) a power electronic building block (PEBB); and (iii) a notional all‐electric ship. The same mathematical model was used to analyze problems (ii) and (iii), that is, the thermal management of heat‐generating equipment packaging. In the examples, the converged mesh had a total of 20, 2000, and 7725 volume elements. The third problem led to the largest simulation, which for steady‐state cases took between 5 and 10 min of computational time to reach convergence and for the ship dynamic response 50 min (i.e., 80,000 s of real time). The regenerative heat exchanger model demonstrated how VEM allowed for the coexistence of different phases (subsystems) within the same volume element. The thermal management model was adjusted and experimentally validated for the PEBB system, and it was possible to perform a parametric and dynamic analysis of the PEBB and of the notional all‐electric ship. Therefore, because of the observed combination of accuracy and low computational time, it is expected that the model could be used as an efficient tool for design, control, and optimization in energy systems engineering. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimization of single SOFC structural design for maximum power

This paper improves previously published models by the authors for a single solid oxide fuel cell (SOFC), and introduces a procedure to optimize its external configuration and operating conditions, so that the net power is maximized. The previous models are hereby improved to include: i) a constant offset overpotential in total potential drop; ii) heat generation associated with all the potential losses; iii) temperature-dependent thermo-physical properties of fuel and air, and iv) pumping power to maximize fuel cell performance. The thermodynamic model is derived from physical laws (e.g., the first law of thermodynamics, Fick's law, Fourier's law) to obtain the temperature and pressure spatial distribution in the SOFC. The electrochemical model is validated by direct comparison with experimental data from the Pacific Northwest National Laboratory (PNNL), and allows for the computation of the SOFC voltage, current, and power output. Based on the simulation results, the structural design, the active three phase boundaries regions at the electrodes and the fuel utilization factor, and their impact on the SOFC performance are discussed. Subjected to fixed total volume, the optimal geometric and operating parameters are pursued so that the net power of the SOFC is maximized through a 4-way-optimization procedure. The method used is general and the numerically obtained maxima are sharp, taking into account that up to a 631% single SOFC performance variation was observed within the studied parameters' range. The fixed volume constraint was then relaxed, and the effect of total volume variation on performance was investigated, delivering the general optimal parameters for the 4-way maximized SOFC net power output within the studied total dimensionless fuel cell volume range. These findings show the potential to use the model as a tool for future SOFC design, simulation and optimization.