Error correcting codes from quasi-Hadamard matrices

Levenshtein described in [5] a method for constructing error correcting codes which meet the Plotkin bounds, provided suitable Ha- damard matrices exist. Uncertainty about the existence of Hadamard matrices on all orders multiple of 4 is a source of difficulties for the prac- tical application of this method. Here we extend the method to the case of quasi-Hadamard matrices. Since efficient algorithms for constructing quasi-Hadamard matrices are potentially available from the literature (e.g. [7]), good error correcting codes may be constructed in practise. We illustrate the method with some examples.Junta de Andalucía FQM–29

Determinants of (–1,1)-matrices of the skew-symmetric type: a cocyclic approach

An n by n skew-symmetric type (−1, 1)-matrix K = [ki,j ] has 1’s on the main diagonal and ±1’s elsewhere with ki,j = −kj,i. The largest possible determinant of such a matrix K is an interesting problem. The literature is extensive for n 0 mod 4 (skew- Hadamard matrices), but for n 2 mod 4 there are few results known for this question. In this paper we approach this problem constructing cocyclic matrices over the dihedral group of 2t elements, for t odd, which are equivalent to (−1, 1)-matrices of skew type. Some explicit calculations have been done up to t = 11. To our knowledge, the upper bounds on the maximal determinant in orders 18 and 22 have been improved.Junta de Andalucía FQM-01

Embedding cocylic D-optimal designs in cocylic Hadamard matrices

A method for embedding cocyclic submatrices with “large” determinants of orders 2t in certain cocyclic Hadamard matrices of orders 4t is described (t an odd integer). If these determinants attain the largest possible value, we are embedding D-optimal designs. Applications to the pivot values that appear when Gaussian elimination with complete pivoting is performed on these cocyclic Hadamard matrices are studied.Ministerio de Ciencia e Innovación MTM2008-06578Junta de Andalucía FQM-016Junta de Andalucía P07-FQM-0298

Non-dimensional analysis of experimental pressure drop and energy dissipation measurements in Oscillatory Baffled Reactors

An experimental study is performed to characterize the pressure drop and the power consumption in Oscillatory Baffled Reactors, using dimensionless numbers: the oscillatory Fanning friction factor (f osc ) and the Power number (Po), respectively. Two baffle geometries (one-orifice and three orifices) are tested, for different fluids and oscillating amplitudes. The range of oscillatory Reynolds numbers (Reosc ) tested is 10–1000. Data reduction based on the statistical fitting and the FFT of the pressure drop and velocity signals is introduced to assess the maximum pressure drop and the phase lag between both signals. The new set of experimental data proves the limitations of the conventional models available in the open literature. f osc and Po provide consistent dimensionless results for the different working fluids tested and their trends are clearly related to different flow behaviours: laminar or chaotic flow. Correlations for f osc and Po as a function of Reosc and dimensionless amplitude are obtained.The authors gratefully acknowledge the financial support of the project DPI2015-66493-P by Ministerio de Economía y Competitividad (MINECO, Spain) and the European Regional Development Fund (ERDF)

Determinants of working capital management

This paper analyzes the determinants of working capital management (WCM) for a sample of Spanish firms during the period 1997-2004. We find that firms have a target investment in working capital and that they take decisions in order to achieve this. The results appear to support the hypothesis that the working capital competes with investment in fixed assets for the funds of the firms when they have financial constraints. Finally, we also find that WCM depends on bargaining power and other financial factors such as the availability of internal finance, cost of financing and financial constraints.Research Agency of the Spanish Government ECO2008-06179/ECO

Efecto de dos citocininas y un inhibidor del crecimiento en la tuberización in vitro de dos genotipos de Solanum tuberosum L. vars. Atlantic y Alpha

This investigation was carried out to evaluate the effect of two cytokinins: 6-benzilaminopurine (BAP) (6.5 mg l-1) and kinetin (K) (2.5 mg l-1), as well as the growth inhibitor abscisic acid (ABA) (1.0 mg l-1) on the in vitro tuberization capacity of two potato varieties: Atlantic and Alpha. The basal culture medium MS (1962) was used as a control. The responses were different between varieties. In cv. Atlantic, the analysis of the number (NM), weight (WM) and diameter (DM) of microtubers indicated that the addition of growth regulators did not affect induction and development of microtubers. However, when BAP was used, a non-significant increment of 41 % was observed in the number of the microtubers compared to the control treatment, from 2.6 to 4.4. The addition of cytokinins and ABA to the medium did not have a significant impact on the development of microtubers. In cv. Alpha the cytokinins used without ABA increased the number of microtubers, which were larger and heavier than those of the control treatment. In this variety, ABA significantly reduced the values of the NM, WM and DM variables. The exogenous action of cytokinins in the culture medium is likely to have caused an endogenous hormonal imbalance in the Atlantic and Alpha genotypes which interfered with their innate microtuberization ability, a result that was even more evident for cv. Alpha, which showed the need to continue optimizing protocols of genotype-specific systems in potato tissue culture to increase yield and seed quality.La presente investigación se llevó a cabo con el objetivo de evaluar el efecto de dos citocininas 6-benzilaminopurina (BAP) (6.5 mg l-1) y kinetina (K) (2.5 mg l-1), más un inhibidor de crecimiento ácido abscísico (ABA) (1.0 mg l-1) sobre la capacidad de tuberización in vitro de dos variedades de papa, Atlantic y Alfa. El medio de cultivo usado como testigo fue el básico MS (1962) sin reguladores del crecimiento. Los resultados obtenidos evidenciaron una respuesta diferente entre variedades. En la variedad Atlantic, el análisis de los datos en relación con las variables número (NM), peso (PM) y diámetro (DM) de microtubérculos indicó que la adición de reguladores de crecimiento no afectó favorablemente la inducción y el desarrollo de microtubérculos, con respecto al testigo. Al utilizar BAP, se notó un incremento no significativo de 41 % en el número promedio de microtubérculos en comparación con el tratamiento control, pasando de 2.6 a 4.4. La adición de citocininas y ABA al medio no provocó efectos positivos en el desarrollo de los microtubérculos. En la variedad Alfa, la utilización de citocininas en ausencia de ABA estimuló el NM y estos fueron más pesados y de mayor diámetro que en el tratamiento testigo. En esta variedad, el ABA causó un efecto negativo en el NM, así como en las variables PM y DM. Probablemente la acción exógena de las citocininas en los medios de cultivo ocasionó un desbalance hormonal endógeno en los genotipos Atlantic y Alfa, que interfirió sobre la capacidad innata de microtuberización, resultado que se evidenció en mayor magnitud para la variedad Alfa, lo cual reveló la necesidad de continuar optimizando los protocolos genotipo-específicos de los sistemas de cultivo de tejidos en papa para aumentar el rendimiento y la calidad de la semilla

Rooted Trees Searching for Cocyclic Hadamard Matrices over D4t

A new reduction on the size of the search space for cocyclic Hadamard matrices over dihedral groups D4t is described, in terms of the so called central distribution. This new search space adopt the form of a forest consisting of two rooted trees (the vertices representing subsets of coboundaries) which contains all cocyclic Hadamard matrices satisfying the constraining condition. Experimental calculations indicate that the ratio between the number of constrained cocyclic Hadamard matrices and the size of the constrained search space is greater than the usual ratio.Ministerio de Ciencia e Innovación MTM2008-06578Junta de Andalucía FQM–296Junta de Andalucía P07-FQM-0298

Validation of a new methodological approach for the selection of wire-coil inserts in thermal equipment

The use of wire-coils is especially relevant at low Reynolds numbers (below the critical number to turbulent flow in smooth tubes) according to its inherent positive features such as the advance of transition onset and, if they present suitable geometric characteristics, the establishment of an extended transitional flow in a critical Reynolds number interval [ReCL − ReCT ], with a predictable friction coefficient and Nusselt number. This paper presents the experimental validation of a new methodology based on the evaluation of a non-dimensional geometry-based parameter: the TSP (Transition Shape Parameter) that allows to predict the friction coefficient evolution with wire-coil inserts and enables to compute the extension of the transitional flow region. The close relationship between hydraulic and thermal performance of wire-coil inserts makes this methodology a valuable tool for selecting the most appropriate wire-coil geometry for a given tubular heat exchanger. It is observed that to promote an increase in heat transfer, the value of the ReCL of the wire coil must be less than the operating Reynolds number range of the equipment. Thus, the ReCL − ReCT interval of the insert should fall into this range. In order to validate the methodological approach, an application to harp-type solar thermal collectors with typical Reynolds number range [40–6000] is presented. Four representative wire-coils, with a wide geometrical range characterized by TSP values of 759, 196, 35.3 and 3.1 (exhibiting significant differentiated behaviours in their friction factor curves and critical Reynolds numbers) were inserted inside the risers of a modified solar collector and experimentally tested at laboratory conditions. Static temperature at different locations at the absorber plate, and pressure drop were measured to obtain friction factor and Nusselt number inside riser covering the laminar, transitional and low-turbulent regions. For a general application with friction factor constraints the most suitable wire-coil geometry is the TSPW02 = 196 with a range of critical Reynolds number of ReCL = 663 and ReCT = 2286 and Nuw02/Nus = 2.21 for Re = [300 − 3000] with f w02/fs = 3, 82. However, for the case study presented (a harp-type solar collector) it is feasible to insert the third wire-coil geometry TSPW03 = 35.3 due to its early transition, with a range of critical Reynolds number of ReCL = 364 and ReCT = 2324, and Nuw/Nus = 1.35 for Re = 300 with a high friction factor augmentation f w03/fs = 18.84. This geometry also promotes the highest absorber temperature reduction. The greatest temperature reduction is observed in the range of Reynolds numbers [700–2000], reaching approximately 6 ◦C, which represents approximately 15 %The authors gratefully acknowledge to European Regional Development Fund and Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación for the financial support of the project ALTES: “Active Latent Thermal Energy Storage”, Ref. PGC2018-100864-B-C21

Experimental correlations on critical Reynolds numbers and friction factor in tubes with wire-coil inserts in laminar, transitional and low turbulent flow regimes

This paper analyses 23 circular helicoidal wire-coils with different geometric characteristics ranging from: dimensionless pitch p/d = [0.25–3.37], dimensionless thickness e/d = [0.071–0.286] and a Reynolds number interval from 50 to 8000. This interval widely includes the Reynolds number range in which rigid wire-coil inserts present better performance as passive enhancement technique for tubular heat exchanger applications Re = [200–2000]. Based on their hydraulic performance, the wire-coil inserts are categorized according to a new dimensionless parameter: the Transition Shape Parameter (TSP). A new set of correlations are obtained to predict the Fanning friction factor coefficient as a function of Reynolds number and geometrical characteristics of the insert within the three flow regimes: laminar, transitional and low turbulent. Additional correlations are proposed to estimate the critical Reynolds number at the beginning and ending of the transition region, which allows to select the most adequate friction factor correlation as a function of the operational Reynolds number for a heat exchanger design application. Finally, a comparative between the proposed and the published correlations in the open literature for laminar and turbulent regimes is presented. This brings to light the need and interest of having the suitable and reliable set of correlations presented in this paper to compute the friction coefficient covering all the wire-coil applicability range as an enhancement technique.The authors gratefully acknowledge the “Fundación Séneca” (Fundación Séneca: Project with Ref. 15297/PI/10) and the Spanish Ministry of Science (Project with Ref. ENE2011-28571-C02-01) for supporting this research