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A Multi-Response Optimization of Thrust Forces, Torques, and the Power of Tapping Operations by Cooling Air in Reinforced and Unreinforced Polyamide PA66
(MDPI, 2018-03-20) Domingo Navas, María Rosario; Agustina Tejerizo, Beatriz De; Marín Martín, Marta María
The use of cooling air during machining is an environmentally conscious procedure, and its applicability to different processes is a research priority. We studied tapping operations, an important operation in the assembly process, using cooling air with unreinforced polyamide (PA66) and polyamide reinforced with glass fiber (PA66-GF30). These materials are widely used in industry, but their behavior with respect to tapping has not been studied. We analyze the outcomes regarding the thrust force, torque, and power at cutting speeds between 15 and 60 m/min. The experimental tests were executed using cooling air at 22 °C, 2 °C, and −18 °C in dry conditions. The M12 × 1.75 mm taps were high-speed steel, with cobalt as the base material and coatings of TiN and AlCrN. To identify the more influential factors, an analysis of variance was performed, along with multi-response optimization to identify the desirability values. This optimization shows that the optimum for PA66can be found in environments close to 3 °C, while the optimum for PA66-GF30 is found at the minimal temperature studied (−18 °C). Thus, cooling air can be considered an adequate procedure for tapping operations, to increase the sustainability of the manufacturing processes.
A new design of multi-tube receiver for Fresnel technology to increase the thermal performance
(Elsevier, 2022-03-05) Abbas, Rubén; Montes Pita, María José; Barbero Fresno, Rubén; Rovira de Antonio, Antonio José
Solar heat for industrial processes is a promising way to meet the high thermal demand required by the industry, while this application becomes an important niche market for solar technology. In this research line, it is proposed a novelty concept based on a rotary Fresnel solar collector to supply heat above 150 °C. This work is focused on the multi-tube receiver for this Fresnel collector, proposing a thermal design based on three criteria that can be generalized for any multi-tube receiver: the fluid flow layout is arranged to meet the symmetry of the solar flux map; the fluid circulates from the lower to the higher flux density zone; and the fluid velocity is modified by modifying the tube diameter, to optimize the heat transfer. Following these criteria, the final configuration of the receiver is chosen based on an exergy optimization, in which both heat loss and pressure drop must be quantified. It has been also accomplished a generalization of the optimization methodology for Fresnel collectors providing heat at different temperatures, showing that, in these cases, the configuration that maximizes the exergy efficiency does not correspond to the one with the highest energy efficiency. This thermal design method can be applied to multi-tube receivers working at higher temperatures in longer Fresnel loops, in which case the optimization will result in more marked differences between the optimal values and the standard ones.
A new method for calculating conduction response factors for multilayer constructions based on frequency–Domain spline interpolation (FDSI) and asymptotic analysis
(Elsevier, 2017-08-01) Sanza Pérez, Javier; Chicote, Manuel Andrés; Velasco Gómez, Eloy; Varela Díez, Fernando
Conduction heat transfer through building construction elements is one of the main components of space heating and cooling loads, and, thus, one of the key aspects when planning sustainable energy designs in the building sector. The Response Factors (RF) method sets the base for related dynamic calculations implemented by most well-known Building Energy Simulation (BES) software, and it represents a research topic of present interest. In this regard, this work introduces a new method for calculating conduction Response Factors in building multilayer constructions, based on the definition of an approximated wall model through Frequency–Domain Spline Interpolation (FDSI) and asymptotic analysis. Its conceptual development as well as first validations comparing with existing methods from previous literature are presented. Finally, as a result of applying a table-lookup approach and the possibility of pre-calculating most of the involved operations, an accurate, fast and easy-to-code algorithm is obtained, which constitutes a promising alternative to improve the current state-of-art calculation procedures.
A New Thermodynamic Model to Approximate Properties of Subcritical Liquids
(MDPI, 2023-06-29) Sánchez Orgaz, Susana; González Fernández, M. Celina; Varela Díez, Fernando; Rodríguez Laguna, Javier
In order to obtain the thermodynamic properties of compressed liquids, it is usual to consider them as incompressible systems, since liquids and solids are well represented by this thermodynamic model. Within this model, there are two usual hypotheses that can be derived in two different submodels: the strictly incompressible (SI) model, which supposes a constant specific volume 𝑣=𝑣0, and a more general model, called temperature-dependent incompressible (TDI) model, which relates a specific volume to temperature, 𝑣=𝑣(𝑇). But, usually, this difference ends here in the thermal equation of state, and only the SI model was developed for caloric and entropic equations. The aim of this work is to provide a complete formulation for the TDI model and show where it can be advantageously used rather than the SI model. The study concludes that the proposed model outperforms the traditional model in the study of subcritical liquid. One conceivable utilization of this model is its integration into certain thermodynamic calculation software packages (e.g., EES), which integrate the more elementary SI model into its code for certain incompressible substances.
A novel energy conversion system based on supercritical CO2 recompression Brayton power cycle for power tower concentrating solar plants
(Elsevier, 2020-02-09) Linares Hurtado, José Ignacio; Cantizano, Alexis; Sánchez, Consuelo; Montes Pita, María José
Power tower concentrating solar plants with thermal energy storage will play a key role in the transition to a low carbon scenario, thanks to be a dispatchable renewable energy system. The ternary MgCl2/KCl/NaCl salt appears as one of the most promising due to its lower melting point, higher heat capacity, lower cost and stability up to 800 °C. A cavity-type receiver has been selected because minimizes radiation heat loss at high working temperatures, compared to an external-type receiver, since all commercial selective coatings degrade in air. Supercritical Brayton power cycle is chosen for the power block because it can surpass 50% efficiency, even when working in dry cooling conditions, and printed circuit heat exchangers are usually recommended due to its ability to support the high pressures. However, plugging/clogging issues arise in their small channels when using molten salts. This paper proposes a novel supercritical CO2 Bayton power cycle whose heat power is supplied through the low pressure side (over 85 bar) allowing the use of shell and tube heat exchangers, achieving a higher compactness and a lower investment. Thus, different options based on the recompression layout with intercooling and reheating have been investigated in both dry and wet cooling scenarios. Reheating is recommended for wet cooling, reaching 54.6% efficiency and an investment of 8662 $/kWe; intercooling with reheating is the best option for dry cooling, reaching 52.6% efficiency and an investment of 8742 $/kWe.
A novel method for the determination of fatty acid esters in aqueous emulsion on Ti6Al4V surface with IRRAS and carbon quantification
(Elsevier, 2018-12-01) Benedicto Bardolet, Elisabet; Carou Porto, Diego; Batlle, L.; Rubio Alvir, Eva María
A novel direct method based on infrared reflection absorption spectroscopy (IRRAS) and carbon elemental analysis has been developed for the quantitative determination of fatty acid ester on Ti6Al4V surface. The new approach involves the IR spectra and carbon analysis of a Ti6Al4V strip treated with a surfactant and ester emulsion adjusted to pH 9.2 with 2-aminoethanol. The results are dependent on the ester and surfactant concentration. The analytical signals are the integral value of the CH2 and CO signals of the IR spectra and the carbon content. The main advantage of the proposed method is that the analysis made directly on the metal surface allows knowing the film forming ability of the emulsion. The method may be useful for research and development of more environmentally friendly water-based metalworking fluids for the metal industry.
A solar air-cooled high efficiency absorption system in dry hot climates: Reduction of water consumption and environmental impact
(VINČA Institute of Nuclear Sciences, 2018) Lizarte, Raquel; Palacios Lorenzo, María Esther; Blanco Marigorta, Ana María; Marcos del Cano, José Daniel; Varela Díez, Fernando
A solar cooling system with an optimized air-cooled double-effect water/LiBr absorption machine is proposed as a sustainable alternative to meet cooling demands in dry hot climates. This system allows eliminating the cooling towers in those regions of the planet where water is scarce. This work analyses the environmental benefits of this air-cooled system, as well as its environmental foot-prints, compared to a solar water-cooled single effect. In this regard, a methodology has been applied to calculate the annual saving in water consumption produced in a case study: a hospital located in Almería, in South of Spain. Further-more, the reduction in energy consumption and CO2 emissions is also quantified since this machine can be driven by solar energy and with higher efficiency than those of single effect.
A unified concept of approximate and quasi efficient solutions and associated subdifferentials in multiobjective optimization
(Springer Nature, 2020-11-18) Jiménez, B.; Luc, D. T.; Novo, V.; Huerga Pastor, Lidia
In this paper, we introduce some new notions of quasi efficiency and quasi proper efficiency for multiobjective optimization problems that reduce to the most important concepts of approximate and quasi efficient solutions given up to now. We establish main properties and provide characterizations for these solutions by linear and nonlinear scalarizations. With the help of quasi efficient solutions, a generalized subdifferential of a vector mapping is introduced, which generates a number of approximate subdifferentials frequently used in optimization in a unifying way. The generalized subdifferential is related to the classical subdifferential of real functions by the method of scalarization. An application of generalized subdifferential to express optimality conditions for quasi efficient solutions is also given.
Acetylene absorption by ionic liquids: A multiscale analysis based on molecular and process simulation
(Elsevier, 2018-10-02) Bedia, Jorge; Moreno, D.; Moya, C.; Riva Silva, Juan de; Larriba, M.; Palomar Herrero, José Francisco; Santiago Lorenzo, Rubén
A COSMO-based/Aspen Plus multiscale simulation methodology was used to evaluate a wide variety of ionic liquids (ILs), more than 300, as potential acetylene absorbents. First, by means of Conductor-like-Screening Model for Real Solvents (COSMO-RS) method, molecular simulations were conducted to select ILs with adequate thermodynamic (Henry’s law constants) and kinetic (diffusion coefficients) properties as acetylene absorbents, using N,N-dimethylformamide (DMF) as benchmark industrial solvent for such solute absorption. Then, the operating units of acetylene absorption of an acetylene and argon mixture, and exhausted solvent regeneration were modeled in Aspen Plus. Simulations of absorption column using equilibrium based design model demonstrated that at least two ILs (1-butyl-3-methylimidazolium cation and acetate and sulfonate anions) present competitive solvent performance in acetylene absorption respect to DMF. In contrast, process analyses with a more realistic rate-based column model revealed that the mass transfer rate clearly controls the acetylene absorption with ILs compared to DMF, due to their viscosity differences. Finally, modeling solvent regeneration stage showed clear advantages of using ILs as acetylene absorbents since efficient acetylene recovery is achieved by flash distillation (vacuum pressure and temperature increase), operation hindered in the case of DMF due to is high volatility, requiring the solvent regeneration by a distillation equipment with higher operating and investment costs. Current COSMO-based/Aspen Plus approach has been demonstrated useful to perform preliminary analyses of the potential application of ILs in new separation processes, before starting with experimental essays, highly demanding in cost and time.
Adaptive model predictive control for electricity management in the household sector
(Elsevier, 2022-05) Muñoz Gómez, Antonio Miguel; Rosales Asensio, Enrique; Fernández Aznar, Gregorio; Galán Hernández, Noemi; Colmenar Santos, Antonio
This paper focuses on the optimisation of electricity consumption in residential buildings. To deal with the increase in electricity consumption, the intermittency of renewable energy generation and grid contingencies, a greater effort is required towards residential management optimisation. A novel adaptive model predictive control algorithm is proposed to achieve this objective. The challenges for this research included recognising and modelling the economic and technical constraints of the sources and appliances and addressing the uncertainties concerning the weather and user behaviour. Data-driven models are developed and trained to predict the user behaviour and buildings. Artificial neural networks and statistical models based on the weighted moving average are proposed to capture the patterns of deferrable and non-deferrable appliances, battery storage, electric vehicles, photovoltaic modules, buildings and grid connections. A dual optimisation method is devised to minimise the electricity bill and achieve thermal comfort. The proposed optimisation solver is a two-step optimisation method based on genetic algorithm and mixed integer linear programming. A comprehensive simulation study was carried out to reveal the effectiveness of the proposed method through a set of simulation scenarios. The results of the quantitative analysis undertaken as part of this study show the effectiveness of the proposed algorithm towards reducing electricity charges and improving grid elasticity.
Advanced thermodynamic cycles for finite heat sources: proposals for closed and open heat sources applications
(Elsevier, 2020) Sánchez, Consuelo; Rovira de Antonio, Antonio José; Muñoz Domínguez, Marta; Barbero Fresno, Rubén
This paper analyses two non-conventional thermodynamic cycles designed to work with finite heat sources, which are suitable for maximum temperatures of about 400 °C. The Hybrid Rankine-Brayton (HRB) cycle fits well to closed heat sources and, in the paper, it is analysed considering its exergy efficiency and some requirements for the maximum and minimum temperature of the heat transfer fluid that feeds the cycle, obtaining promising results. The other one is a new proposal called Recuperated and Double Expanded (RDE) cycle, aimed to translate the good features of HRB from closed heat sources to open ones, where the performance of HRB is limited. Both cycles are compared to some reference ones. Results show that the HRB cycle is a good candidate for finite closed heat sources, particularly with maximum temperature around 400 °C and with temperature changes of the heat transfer fluid from 100 °C to 150 °C. The RDE cycle exhibits good performance for finite open heat sources with maximum temperatures between 200 °C and 400 °C, and it behaves similarly to tri-lateral cycles.
Advances in solar thermal power plants based on pressurised central receivers and supercritical power cycles
(Elsevier, 2023-07-28) Guedez Mata, Rafael; Linares Hurtado, José Ignacio; Reyes Belmonte, Miguel Ángel; Montes Pita, María José
This work addresses the comparative thermo-economic study of different configurations of solar thermal power plants, based on supercritical power cycles and pressurised central receiver systems. For all the cases examined, two innovations are introduced in the solar subsystem, compared to other similar studies. Firstly, the heat transfer fluid in the receiver is either a pressurised gas or a supercritical fluid. Secondly, the receiver is composed of compact structures performing as absorber panels, arranged in a radial configuration. The investigation considers different supercritical CO2 recompression cycles of 50 MWe, including a novel proposal of a directly coupled cycle with heat input downstream of the turbine. Furthermore, the study evaluates different heat transfer fluids in the receiver, specifically CO2, N2, and He, concluding that the former is preferred due to its better thermal performance. The main results show that an increase in the receiver inlet pressure yields to a reduction in its size, favouring the thermal efficiency but penalising the optical efficiency of the solar field. Therefore, optimal working pressures may exist for each configuration, depending on the operating temperature. When comparing the optimal configurations, it is observed that the plant based on the intercooling cycle demonstrates the highest overall efficiency, reaching 32.05%. At last, an economic analysis is conducted to assess the viability of the identified optimal configurations. In this regard, the plant based on the partial-cooling cycle exhibits the lowest levelised cost of electricity at 0.15 $/kWh. This is primarily due to its lower investment cost. The innovative directly coupled cycle follows closely with a cost of 0.17 $/kWh, driven by its high electricity production resulting from its low self-consumption.
Analysis and comparison of Integrated Solar Combined Cycles using parabolic troughs and linear Fresnel reflectors as concentrating systems
(Elsevier, 2015-11-12) Abbas, Rubén; Rovira de Antonio, Antonio José; Barbero Fresno, Rubén; Montes Pita, María José; Varela Díez, Fernando
This paper compares the annual performance and economic feasibility of Integrated Solar Combined Cycles (ISCC) using two solar concentration technologies: parabolic trough collectors (PTC) and linear Fresnel reflectors (LFR). Integration of solar energy to the steam turbine of a combined cycle gives some advantages: the first one is the fuel saving due to the solar contribution and, additionally, the second one is that this contribution takes place especially in highly insolated periods with high ambient temperatures, when conventional combined cycles decrease their power rate and work with decreased efficiency. Previous works showed the convenience of ISCC using PTC and direct steam generation in locations with severe climatology. Besides, LFR technology is currently considered as a good option for reducing the cost of concentrating solar power. Thus, in the present work both concentrating technologies are studied and compared. Solar contribution is only used for evaporating water, increasing the production of the high pressure level of the steam generator. Two locations, Almeria and Las Vegas, are selected for the annual analyses. Results show that the proposed evaporative configurations increase the annual performance. Also, the thermal contribution is higher with PTC, but LFR may improve the economic feasibility of the plant.
Analysis and diagnosis of risk-prevention training actions in the Spanish construction sector
(Elsevier, 2018-07) Romero Barriuso, Álvaro; Segarra Cañamares, M.; González García, María de las Nieves; Rodríguez Sáiz, Ángel; Villena Escribano, Blasa María::virtual::6760::600; Villena Escribano, Blasa María; Villena Escribano, Blasa María; Villena Escribano, Blasa María
The aim of this research paper is to analyze occupational risk-prevention training in Small and Medium Enterprises (SMEs) in the Spanish Construction Sector. To do so, an in-depth study is completed on compliance with the entrepreneurial obligation to inform and to train workers in occupational risk-prevention, in accordance with the regulations laid down in Directive 89/391/EEC, and transposed into Spanish Law in Act 31/1995, of 8 November, on Risk Prevention in the Workplace [Ley de Prevención de Riesgos Laborales (LPRL)]. Three questionnaires were designed and two discussion groups were organized with risk-prevention trainers and business representatives in the sector. Databases from various bodies were jointly consulted, specifically the External Prevention Services (EPS) and the Construction Labour Foundation [Fundación Laboral de la Construcción] (CLF), to establish both the weaknesses and the strengths of occupational risk-prevention training and the training systems of the firms in the sector. Having gathered all the information, the strategic indicators of training in risk-prevention were analyzed, such as the professional qualifications of the trainers, the training methodologies employed, and the training and information that the worker received on the job. The results showed that the majority of trainers in charge of training courses were not construction specialists, the training courses were not adapted to the training level of the workers and, importantly, the teaching materials were never in the other languages of the foreign workers. In conclusion, higher levels of professionalization are necessary for all the agents involved in risk-prevention procedures and construction processes.
Analysis of an Integrated Solar Combined Cycle with Recuperative Gas Turbine and Double Recuperative and Double Expansion Propane Cycle.
(MDPI, 2020) Abbas, Rubén; Sebastián, Andrés; Rovira de Antonio, Antonio José; Muñoz Domínguez, Marta
The main objective of this paper is to present and analyze an innovative configuration of integrated solar combined cycle (ISCC). As novelties, the plant includes a recuperative gas turbine and the conventional bottoming Rankine cycle is replaced by a recently developed double recuperative double expansion (DRDE) cycle. The configuration results in a fuel saving in the combustion chamber at the expense of a decreased exhaust gas temperature, which is just adequate to feed the DRDE cycle that uses propane as the working fluid. The solar contribution comes from a solar field of parabolic trough collectors, with oil as the heat transfer fluid. The optimum integration point for the solar contribution is addressed. The performance of the proposed ISCC-R-DRDE design conditions and off-design operation was assessed (daily and yearly) at two different locations. All results were compared to those obtained under the same conditions by a conventional ISCC, as well as similar configurations without solar integration. The proposed configuration obtains a lower heat rate on a yearly basis in the studied locations and lower levelized cost of energy (LCOE) than that of the ISCC, which indicates that such a configuration could become a promising technology.
Analysis of Favourable Process Conditions for the 2 Manufacturing of Thin-Wall Pieces of Mild Steel 3 Obtained by Wire and Arc Additive Manufacturing 4 (WAAM)
(2018) Prado Cerqueira, José Luis; Diéguez, José Luis; Aragón, Ana María; Lorenzo Martín, Cinta; Yanguas Gil, Ángel; Rodríguez Prieto, Álvaro
One of the challenges in additive manufacturing (AM) of metallic materials is to obtain workpieces free of defects with excellent physical, mechanical, and metallurgical properties. In wire and arc additive manufacturing (WAAM) the influences of process conditions on thermal history, microstructure and resultant mechanical and surface properties of parts must be analyzed. In this work, 3D metallic parts of mild steel wire (American Welding Society-AWS ER70S-6) are built with a WAAM process by depositing layers of material on a substrate of a S235 JR steel sheet of 3 mm thickness under different process conditions, using as welding process the gas metal arc welding (GMAW) with cold metal transfer (CMT) technology, combined with a positioning system such as a computer numerical controlled (CNC) milling machine. Considering the hardness profiles, the estimated ultimate tensile strengths (UTS) derived from the hardness measurements and the microstructure findings, it can be concluded that the most favorable process conditions are the ones provided by CMT, with homogeneous hardness profiles, good mechanical strengths in accordance to conditions defined by standard, and without formation of a decohesionated external layer; CMT Continuous is the optimal option as the mechanical properties are better than single CMT.
Analysis of Force Signals for the Estimation of Surface Roughness during Robot-Assisted Polishing
(MDPI, 2018-08-15) Teti, Roberto; Agustina Tejerizo, Beatriz De; Marín Martín, Marta María; Rubio Alvir, Eva María
In this study feature extraction of force signals detected during robot-assisted polishing processes was carried out to estimate the surface roughness during the process. The purpose was to collect significant features from the signal that allow the determination of the end point of the polishing process based on surface roughness. For this objective, dry polishing turning tests were performed on a Robot-Assisted Polishing (RAP) machine (STRECON NanoRAP 200) during three polishing sessions, using the same polishing conditions. Along the tests, force signals were acquired and offline surface roughness measurements were taken at the end of each polishing session. As a main conclusion, it can be affirmed, regarding the force signal, that features extracted from both time and frequency domains are valuable data for the estimation of surface roughness.
Analysis of internal heat recovery capability in air-cooled indirect fired GAX-based absorption chiller in part-load operation
(Elsevier, 2024-02-15) Palacios Lorenzo, María Esther; Marcos del Cano, José Daniel
Single-effect absorption chillers are the most popular because of their low cost, despite their low COP. Among them, GAX-based AirCooled absorption chillers are very interesting because they have improved COP because of their ability to recover internal heat at low thermal lifts. This workshop analysed the ability of these types of chillers to recover internal heat at high thermal lifts by changing the pressure drop of an extra valve, a feature of the Robur absorption chiller when operating in subzero applications. The complete differential mathematical model analyses the components involved in heat supply and recovery and provides information on their operation. A thorough assessment of exergy destruction in the absorption refrigeration system was carried out. The main results show that when the chiller is driven at a temperature of 210 °C and an ambient temperature of 40 °C, a rise in the pressure drop of the additional valve, ΔPval1, from 175 to 700 kPa causes the extension of the vapour purification process to be reduced by 13.7% in the column of distillation and by 70.6% in the rectifier. Despite the adverse effect of ΔPval1 increase on the cooling capacity, there is no risk that the distillation column operates in weeping mode. However, this adjustment increases the internal thermal load of the generator by 26.9%. Furthermore, the mass fraction of the refrigerant flow is very similar. In addition, the occurrence of a two-phase solution flow at the input of a solution cooling absorber is the practical upper limit of ΔPval1. The refrigerant flow in the solution cooling absorber is reduced by 21.3%. Finally, the contribution of the heat recovery loop to the total exergy destruction in the refrigeration system rises slightly by 2.7% when ΔPval1 increases due to the contribution of the vapour purification system, which increases at the expense of that of the re-boiler and the SolutionCooled absorber. The results of this study show to what extent the modified GAX-based cycle can function effectively at high thermal lifts.
Analytical and numerical study for selecting polymeric matrix composites intended to nuclear applications
(SAGE, 2019-12) Merayo, David; Rodríguez Prieto, Álvaro; Camacho López, Ana María
This study describes a methodological proposal to select composite materials which are suitable to be employed to manufacture pipes that can properly withstand environments subjected to gamma and neutronic radiation. The methodology is used to select, among many others, the optimal composite material whose properties are used afterwards to simulate several pipe sections by finite element analysis, comparing the results with a well-known nuclear-grade steel, WWER 15Kh2MFAA. The most suitable composite material according to the defined criteria is composed of a phenolic resin matrix reinforced with long boron fibres and exhibit great properties to be used in a nuclear reactor environment: good radiation resistance and mechanical properties with a very low density at low cost. It can be concluded that, in some cases, composite material pipes can be a better option than steel ones. Extending the method to be employed in other industries or with other components could be seen as future works.
Approximate solutions of vector optimization problems via improvement sets in real linear spaces
(Springer Nature, 2018-04) Gutiérrez, C.; Jiménez, B.; Novo, V.; Huerga Pastor, Lidia::virtual::4610::600; Huerga Pastor, Lidia; Huerga Pastor, Lidia; Huerga Pastor, Lidia
We deal with a constrained vector optimization problem between real linear spaces without assuming any topology and by considering an ordering defined through an improvement set E. We study E-optimal and weak E-optimal solutions and also proper E-optimal solutions in the senses of Benson and Henig. We relate these types of solutions and we characterize them through approximate solutions of scalar optimization problems via linear scalarizations and nearly E-subconvexlikeness assumptions. Moreover, in the particular case when the feasible set is defined by a cone-constraint, we obtain characterizations by means of Lagrange multiplier rules. The use of improvement sets allows us to unify and to extend several notions and results of the literature. Illustrative examples are also given.

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