A methodology to compare dimensionality reduction algorithms in terms of loss of quality

Dimensionality Reduction (DR) is attracting more attention these days as a result of the increasing need to handle huge amounts of data effectively. DR methods allow the number of initial features to be reduced considerably until a set of them is found that allows the original properties of the data to be kept. However, their use entails an inherent loss of quality that is likely to affect the understanding of the data, in terms of data analysis. This loss of quality could be determinant when selecting a DR method, because of the nature of each method. In this paper, we propose a methodology that allows different DR methods to be analyzed and compared as regards the loss of quality produced by them. This methodology makes use of the concept of preservation of geometry (quality assessment criteria) to assess the loss of quality. Experiments have been carried out by using the most well-known DR algorithms and quality assessment criteria, based on the literature. These experiments have been applied on 12 real-world datasets. Results obtained so far show that it is possible to establish a method to select the most appropriate DR method, in terms of minimum loss of quality. Experiments have also highlighted some interesting relationships between the quality assessment criteria. Finally, the methodology allows the appropriate choice of dimensionality for reducing data to be established, whilst giving rise to a minimum loss of quality.

Comparative analysis of measurement techniques of the sound absorption coefficient of a material

Las tendencias actuales apuntan al desarrollo de nuevos materiales econ��micos y ecol��gicos con ��ptimas propiedades mec��nicas, ac��sticas y t��rmicas. En la caracterizaci��n ac��stica del material es habitual medir su coeficiente de absorci��n sonora. Las dos t��cnicas usuales de medida de este par��metro son en c��mara reverberante y en tubo de Kundt. No obstante, existen t��cnicas de medida ���in situ��� del coeficiente de absorci��n que permiten una comprobaci��n del comportamiento real en la forma definitiva de colocaci��n del material. En este trabajo se presenta un estudio comparativo del coeficiente de absorci��n sonora medido en un material usando distintas t��cnicas de medida.

Determination of a refractive index and an extinction coefficient of standard production of CVD-graphene

The refractive index and extinction coefficient of chemical vapour deposition grown graphene are determined by ellipsometry analysis. Graphene films were grown on copper substrates and transferred as both monolayers and bilayers onto SiO2/Si substrates by using standard manufacturing procedures. The chemical nature and thickness of residual debris formed after the transfer process were elucidated using photoelectron spectroscopy. The real layered structure so deduced has been used instead of the nominal one as the input in the ellipsometry analysis of monolayer and bilayer graphene, transferred onto both native and thermal silicon oxide. The effect of these contamination layers on the optical properties of the stacked structure is noticeable both in the visible and the ultraviolet spectral regions, thus masking the graphene optical response. Finally, the use of heat treatment under a nitrogen atmosphere of the graphene-based stacked structures, as a method to reduce the water content of the sample, and its effect on the optical response of both graphene and the residual debris layer are presented. The Lorentz-Drude model proposed for the optical response of graphene fits fairly well the experimental ellipsometric data for all the analysed graphene-based stacked structures.

Effect of short-term fasting prior to slaughter on welfare and meat quality or rainbow trout (Oncorhynchus mykiss)

El manejo pre-sacrificio es de vital importancia en acuicultura, ya que afecta tanto a las reacciones fisiol��gicas como a los procesos bioqu��micos post mortem, y por tanto al bienestar y a la calidad del producto. El ayuno pre-sacrificio se lleva a cabo de forma habitual en acuicultura, ya que permite el vaciado del aparato digestivo de restos de alimento y heces, reduciendo de esta manera la carga bacteriana en el intestino y la dispersi��n de enzimas digestivos y potenciales pat��genos a la carne. Sin embargo, la duraci��n ��ptima de este ayuno sin que el pez sufra un estr��s innecesario no est�� clara. Adem��s, se sabe muy poco sobre la mejor hora del d��a para realizar el sacrificio, lo que a su vez est�� regido por los ritmos diarios de los par��metros fisiol��gicos de estr��s. Finalmente, se sabe que la temperatura del agua juega un papel muy importante en la fisiolog��a del estr��s pero no se ha determinado su efecto en combinaci��n con el ayuno. Adem��s, las actuales recomendaciones en relaci��n a la duraci��n ��ptima del ayuno previo al sacrificio en peces no suelen considerar la temperatura del agua y se basan ��nicamente en d��as y no en grados d��a (��C d). Se determin�� el efecto del ayuno previo al sacrificio (1, 2 y 3 d��as, equivalente a 11,1-68,0 grados d��a) y la hora de sacrificio (08h00, 14h00 y 20h00) en trucha arco iris (Oncorhynchus mykiss) de tama��o comercial en cuatro pruebas usando diferentes temperaturas de agua (Prueba 1: 11,8 ��C; Prueba 2: 19,2 ��C; Prueba 3: 11,1 ��C; y Prueba 4: 22,7 ��C). Se midieron indicadores biom��tricos, hematol��gicos, metab��licos y de calidad de la carne. En cada prueba, los valores de los animales ayunados (n=90) se compararon con 90 animales control mantenidos bajo condiciones similares pero nos ayunados. Los resultados sugieren que el ayuno tuvo un efecto significativo sobre los indicadores biom��tricos. El coeficiente de condici��n en los animales ayunados fue menor que en los controles despu��s de 2 d��as de ayuno. El vaciado del aparato digestivo se produjo durante las primeras 24 h de ayuno, encontr��ndose peque��as cantidades de alimento despu��s de 48 h. Por otra parte, este vaciado fue m��s r��pido cuando las temperaturas fueron m��s altas. El peso del h��gado de los animales ayunados fue menor y las diferencias entre truchas ayunadas y controles fueron m��s evidentes a medida que el vaciado del aparato digestivo fue m��s r��pido. El efecto del ayuno hasta 3 d��as en los indicadores hematol��gicos no fue significativo. Los niveles de cortisol en plasma resultaron ser altos tanto en truchas ayunadas como en las alimentadas en todas las pruebas realizadas. La concentraci��n media de glucosa vari�� entre pruebas pero mostr�� una tendencia a disminuir en animales ayunados a medida que el ayuno progresaba. En cualquier caso, parece que la temperatura del agua jug�� un papel muy importante, ya que se encontraron concentraciones m��s altas durante los d��as 2 y 3 de ayuno en animales mantenidos a temperaturas m��s bajas previamente al sacrificio. Los altos niveles de lactato obtenidos en sangre parecen sugerir episodios de intensa actividad muscular pero no se pudo encontrar relaci��n con el ayuno. De la misma manera, el nivel de hematocrito no mostr�� efecto alguno del ayuno y los leucocitos tendieron a ser m��s altos cuando los animales estaban menos estresados y cuando su condici��n corporal fue mayor. Finalmente, la disminuci��n del peso del h��gado (��ndice hepatosom��tico) en la Prueba 3 no se vio acompa��ada de una reducci��n del gluc��geno hep��tico, lo que sugiere que las truchas emplearon una estrategia diferente para mantener constantes los niveles de glucosa durante el periodo de ayuno en esa prueba. En relaci��n a la hora de sacrificio, se obtuvieron niveles m��s bajos de cortisol a las 20h00, lo que indica que las truchas estaban menos estresadas y que el manejo pre-sacrificio podr��a resultar menos estresante por la noche. Los niveles de hematocrito fueron tambi��n m��s bajos a las 20h00 pero solo con temperaturas m��s bajas, sugiriendo que las altas temperaturas incrementan el metabolismo. Ni el ayuno ni la hora de sacrificio tuvieron un efecto significativo sobre la evoluci��n de la calidad de la carne durante los 3 d��as de almacenamiento. Por el contrario, el tiempo de almacenamiento s�� que parece tener un efecto claro sobre los par��metros de calidad del producto final. Los niveles m��s bajos de pH se alcanzaron a las 24-48 h post mortem, con una lata variabilidad entre duraciones del ayuno (1, 2 y 3 d��as) en animales sacrificados a las 20h00, aunque no se pudo distinguir ning��n patr��n com��n. Por otra parte, la mayor rigidez asociada al rigor mortis se produjo a las 24 h del sacrificio. La capacidad de retenci��n de agua se mostr�� muy estable durante el per��odo de almacenamiento y parece ser independiente de los cambios en el pH. El par��metro L* de color se increment�� a medida que avanzaba el per��odo de almacenamiento de la carne, mientras que los valores a* y b* no variaron en gran medida. En conclusi��n, bas��ndose en los resultados hematol��gicos, el sacrificio a ��ltima hora del d��a parece tener un efecto menos negativo en el bienestar. De manera general, nuestros resultados sugieren que la trucha arco iris puede soportar un per��odo de ayuno previo al sacrificio de hasta 3 d��as o 68 ��C d sin que su bienestar se vea seriamente comprometido. Es probable que con temperaturas m��s bajas las truchas pudieran ser ayunadas durante m��s tiempo sin ning��n efecto negativo sobre su bienestar. En cualquier caso, se necesitan m��s estudios para determinar la relaci��n entre la temperatura del agua y la duraci��n ��ptima del ayuno en t��rminos de p��rdida de peso vivo y la disminuci��n de los niveles de glucosa en sangre y otros indicadores metab��licos. SUMMARY Pre-slaughter handling in fish is important because it affects both physiological reactions and post mortem biochemical processes, and thus welfare and product quality. Pre-slaughter fasting is regularly carried out in aquaculture, as it empties the viscera of food and faeces, thus reducing the intestinal bacteria load and the spread of gut enzymes and potential pathogens to the flesh. However, it is unclear how long rainbow trout can be fasted before suffering unnecessary stress. In addition, very little is known about the best time of the day to slaughter fish, which may in turn be dictated by diurnal rhythms in physiological stress parameters. Water temperature is also known to play a very important role in stress physiology in fish but the combined effect with fasting is unclear. Current recommendations regarding the optimal duration of pre-slaughter fasting do not normally consider water temperature and are only based on days, not degree days (��C d). The effects of short-term fasting prior to slaughter (1, 2 and 3 days, between 11.1 and 68.0 ��C days) and hour of slaughter (08h00, 14h00 and 20h00) were determined in commercial-sized rainbow trout (Oncorhynchus mykiss) over four trials at different water temperatures (TRIAL 1, 11.8 ��C; TRIAL 2, 19.2 ��C; TRIAL 3, 11.1 ��C; and TRIAL 4, 22.7 ��C). We measured biometric, haematological, metabolic and product quality indicators. In each trial, the values of fasted fish (n=90) were compared with 90 control fish kept under similar conditions but not fasted. Results show that fasting affected biometric indicators. The coefficient of condition in fasted trout was lower than controls 2 days after food deprivation. Gut emptying occurred within the first 24 h after the cessation of feeding, with small traces of digesta after 48 h. Gut emptying was faster at higher water temperatures. Liver weight decreased in food deprived fish and differences between fasted and fed trout were more evident when gut clearance was faster. The overall effect of fasting for up to three days on haematological indicators was small. Plasma cortisol levels were high in both fasted and fed fish in all trials. Plasma glucose response to fasting varied among trials, but it tended to be lower in fasted fish as the days of fasting increased. In any case, it seems that water temperature played a more important role, with higher concentrations at lower temperatures on days 2 and 3 after the cessation of feeding. Plasma lactate levels indicate moments of high muscular activity and were also high, but no variation related to fasting could be found. Haematocrit did not show any significant effect of fasting, but leucocytes tended to be higher when trout were less stressed and when their body condition was higher. Finally, the loss of liver weight was not accompanied by a decrease in liver glycogen (only measured in TRIAL 3), suggesting that a different strategy to maintain plasma glucose levels was used. Regarding the hour of slaughter, lower cortisol levels were found at 20h00, suggesting that trout were less stressed later in the day and that pre-slaughter handling may be less stressful at night. Haematocrit levels were also lower at 20h00 but only at lower temperatures, indicating that higher temperatures increase metabolism. Neither fasting nor the hour of slaughter had a significant effect on the evolution of meat quality during 3 days of storage. In contrast, storage time seemed to have a more important effect on meat quality parameters. The lowest pH was reached 24-48 h post mortem, with a higher variability among fasting durations at 20h00, although no clear pattern could be discerned. Maximum stiffening from rigor mortis occurred after 24 h. The water holding capacity was very stable throughout storage and seemed to be independent of pH changes. Meat lightness (L*) slightly increased during storage and a* and b*-values were relatively stable. In conclusion, based on the haematological results, slaughtering at night may have less of a negative effect on welfare than at other times of the day. Overall, our results suggest that rainbow trout can cope well with fasting up to three days or 68 ��C d prior to slaughter and that their welfare is therefore not seriously compromised. At low water temperatures, trout could probably be fasted for longer periods without negative effects on welfare but more research is needed to determine the relationship between water temperature and days of fasting in terms of loss of live weight and the decrease in plasma glucose and other metabolic indicators.

Tuning the properties of carbon fiber-reinforced poly (phenylene sulphide) laminates via incorporation of inorganic fullerene-like WS2 nanoparticles

Novel carbon fiber (CF)-reinforced poly(phenylene sulphide) (PPS) laminates incorporating inorganic fullerene-like tungsten disulfide (IF-WS2) nanoparticles were prepared via melt-blending and hot-press processing. The influence of the IF-WS2 on the morphology, thermal, mechanical and tribological properties of PPS/CF composites was investigated. Efficient nanoparticle dispersion within the matrix was attained without using surfactants. A progressive rise in thermal stability was found with increasing IF-WS2 loading, as revealed by thermogravimetric analysis. The addition of low nanoparticle contents retarded the crystallization of the matrix, whereas concentrations equal or higher than 1.0 wt% increased both the crystallization temperature and degree of crystallinity compared to those of PPS/CF. Mechanical tests indicated that with only 1.0 wt% IF-WS2 the flexural modulus and strength of PPS/CF improved by 17 and 14%, respectively, without loss in toughness, ascribed to a synergistic effect between the two fillers. A significant enhancement in the storage modulus and glass transition temperature was also observed. Moreover, the wear rate and coefficient of friction strongly decreased, attributed to the lubricant role of the IF-WS2 combined with their reinforcing effect. These inorganic nanoparticles show great potential to improve the mechanical and tribological properties of conventional thermoplastic/CF composites for structural applications.

Rheological and tribological properties of poly(phenylene sulphide) and poly(ether ether ketone) composites incorporating carbon nanotubes and inorganic nanoparticles: a comparative study

The rheological and tribological properties of single-walled carbon nanotube (SWCNT)-reinforced poly(phenylene sulphide) (PPS) and poly(ether ether ketone) (PEEK) nanocomposites prepared via melt-extrusion were investigated. The effectiveness of employing a dual-nanofiller strategy combining polyetherimide (PEI)-wrapped SWCNTs with inorganic fullerene-like tungsten disulfide (IF-WS2) nanoparticles for property enhancement of the resulting hybrid composites was evaluated. Viscoelastic measurements revealed that the complex viscosity ?, storage modulus G?, and loss modulus G? increased with SWCNT content. In the low-frequency region, G? and G? became almost independent of frequency at higher SWCNT loadings, suggesting a transition from liquid-like to solid-like behavior. The incorporation of increasing IF-WS2 contents led to a progressive drop in ? and G? due to a lubricant effect. PEEK nanocomposites showed lower percolation threshold than those based on PPS, ascribed to an improved SWCNT dispersion due to the higher affinity between PEI and PEEK. The SWCNTs significantly lowered the wear rate but only slightly reduced the coefficient of friction. Composites with both nanofillers exhibited improved wear behavior, attributed to the outstanding tribological properties of these nanoparticles and a synergistic reinforcement effect. The combination of SWCNTs with IF-WS2 is a promising route for improving the tribological and rheological performance of thermoplastic nanocomposites.