2,056 research outputs found
Melting behavior of large disordered sodium clusters
The melting-like transition in disordered sodium clusters Na_N, with N=92 and
142 is studied by using a first-principles constant-energy molecular dynamics
simulation method. Na_142, whose atoms are distributed in two (surface and
inner) main shells with different radial distances to the center of mass of the
cluster, melts in two steps: the first one, at approx. 130 K, is characterized
by a high intrashell mobility of the atoms, and the second, homogeneous
melting, at approx. 270 K, involves diffusive motion of all the atoms across
the whole cluster volume (both intrashell and intershell displacements are
allowed). On the contrary, the melting of Na_92 proceeds gradually over a very
wide temperature interval, without any abrupt step visible in the thermal or
structural melting indicators. The occurrence of well defined steps in the
melting transition is then shown to be related to the existence of a
distribution of the atoms in shells. Thereby we propose a necessary condition
for a cluster to be considered rigorously amorphouslike (totally disordered),
namely that there are no space regions of the cluster where the local value of
the atomic density is considerably reduced. Na_92 is the only cluster from the
two considered that verifies this condition, so its thermal behavior can be
considered as representative of that expected for amorphous clusters. Na_142,
on the other hand, has a discernible atomic shell structure and should be
considered instead as just partially disordered. The thermal behavior of these
two clusters is also compared to that of icosahedral (totally ordered) sodium
clusters of the same sizes.Comment: LaTeX file. 7 pages with 12 picture
Differences in Foliage Affect Performance of the Lappet Moth, Streblote panda: Implications for Species Fitness
Implications for adults' fitness through the foliage effects of five different host plants on larval survival and performance of the lappet moth, Streblote panda Hübner (Lepidoptera: Lasiocampidae), as well as their effect on species fitness were assayed. Larvae were reared under controlled laboratory conditions on excised foliage. Long-term developmental experiments were done using first instar larvae to adult emergence, and performance experiments were done using fifth instar larvae. Survival, development rates, and food use were measured. Foliar traits analysis indicated that leaves of different host plants varied, significantly affecting larvae performance and adult fitness. Pistacia lentiscus L. (Sapindales: Anacardiaceae), Arbutus unedo L. (Ericales: Ericaceae), and Retama sphaerocarpa (L.) Boiss. (Fabales: Fabaceae) were the most suitable hosts. Larvae fed on Tamarix gallica L. (Caryophyllales: Tamaricaceae) and Spartium junceum L. (Fabales: Fabaceae) showed the lowest survival, rates of development and pupal and adult weight. In general, S. panda showed a relatively high capacity to buffer low food quality, by reducing developmental rates and larvae development thereby reaching the minimum pupal weight that ensures adult survival. Less suitable plants seem to have indirect effects on adult fitness, producing smaller adults that could disperse to other habitats
Intervalo entre partos en el vacuno de carne extensivo de raza retinta
La eficacia reproductiva en el vacuno depende, entre otros parámetros, del intervalo entre partos. Esta variable está considerada una de las más importantes para la rentabilidad de la explotación en el caso del vacuno de carne en régimen extensivo. En este trabajo se estudia la influencia de distintos factores sobre el intervalo entre partos en la raza retinta mediante el análisis de 7356 partos de 1803 vacas pertenecientes al Núcleo de Control de Rendimientos de la Asociación de Ganaderos de esta raza. Nuestros resultados muestran que este parámetro se ve afectado principalmente por la ganadería, la campaña ganadera, época, sus interacciones y el tipo de parto, no existiendo relación significativa entre este período y el peso al destete de los terneros El valor medio obtenido para todo el intervalo analizado ha sido de 16,144 ± 0,086 meses y la heredabilidad estimada para este carácter fue de 0,1104 ± 0,08
Effect of Glass Fiber Hybridization on the Behavior Under Impact of Woven Carbon Fiber/Epoxy Laminates
The low-velocity impact behavior was studied in hybrid laminates manufactured by RTM with woven carbon and glass (S2) fabrics. Specimens with different thicknesses and glass fiber content (from 0 to 21 vol.%) were tested with impact energies in the range 30–245 J and the resulting deformation and fracture micromechanisms were studied using X-ray microtomography. The results of these analyses, together with those of the impact tests (maximum load and energy absorbed), were used to elucidate the role played by glass fiber hybridization on the fracture micromechanisms and on the overall laminate performance under low-velocity impact
Greedy seeding procedure for GAs solving a strip packing problem
In this paper, the two-dimensional strip packing problem with 3-stage level patterns is tackled using genetic algorithms (GAs). We evaluate the usefulness of a greedy seeding procedure for creating the initial population, incorporating problem knowledge. This is motivated by the expectation that the seeding will speed up the GA by starting the search in promising regions of the search space. An analysis of the impact of the seeded initial population is offered, together with a complete study of the influence of these modifications on the genetic search. The results show that the use of an appropriate seeding of the initial population outperforms existing GA approaches on all the used problem instances, for all the metrics used, and in fact it represents the new state of the art for this problem.Red de Universidades con Carreras en Informática (RedUNCI
Greedy seeding procedure for GAs solving a strip packing problem
In this paper, the two-dimensional strip packing problem with 3-stage level patterns is tackled using genetic algorithms (GAs). We evaluate the usefulness of a greedy seeding procedure for creating the initial population, incorporating problem knowledge. This is motivated by the expectation that the seeding will speed up the GA by starting the search in promising regions of the search space. An analysis of the impact of the seeded initial population is offered, together with a complete study of the influence of these modifications on the genetic search. The results show that the use of an appropriate seeding of the initial population outperforms existing GA approaches on all the used problem instances, for all the metrics used, and in fact it represents the new state of the art for this problem.Red de Universidades con Carreras en Informática (RedUNCI
Duración de la gestación en el ganado vacuno de raza Retinta
Este trabajo ha sido extraído de la tesina de licenciatura "Duración de la gestación en el ganado vacuno Retinto: Aplicación práctica
en el plan de mejora", realizada por J. M. Pastor y dirigida por A. Molina. Esta fue delendida en la Universidad de Córdoba en
1996, obteniendo la calificación de Sobresaliente
Methodology for measuring exhaust aerosol size distributions using an engine test under transient operating conditions
[EN] A study on the sources of variability in the measurement of particle size distribution using a two-stage dilution system and an engine exhaust particle sizer was conducted to obtain a comprehensive and repeatable methodology that can be used to measure the particle size distribution of aerosols emitted by a light-duty diesel engine under transient operating conditions. The paper includes three experimental phases: an experimental validation of the measurement method; an evaluation of the influence of sampling factors, such as dilution system pre-conditioning; and a study of the effects of the dilution conditions, such as the dilution ratio and the dilution air temperature. An examination of the type and degree of influence of each studied factor is presented, recommendations for reducing variability are given and critical parameter values are identified to develop a highly reliable measurement methodology that could be applied to further studies on the effect of engine operating parameters on exhaust particle size distributions. © 2011 IOP Publishing Ltd.The translation of this paper was funded by the Universidad Politecnica de Valencia, Spain.Desantes, J.; Bermúdez, V.; Molina, S.; Linares Rodríguez, WG. (2011). Methodology for measuring exhaust aerosol size distributions using an engine test under transient operating conditions. Measurement Science and Technology. 22(11):1-14. doi:10.1088/0957-0233/22/11/115101S1142211Dobbins, R. A. (2007). Hydrocarbon Nanoparticles Formed in Flames and Diesel Engines. Aerosol Science and Technology, 41(5), 485-496. doi:10.1080/02786820701225820Davidson, C. I., Phalen, R. F., & Solomon, P. A. (2005). Airborne Particulate Matter and Human Health: A Review. Aerosol Science and Technology, 39(8), 737-749. doi:10.1080/02786820500191348McDonald, J. D., Barr, E. B., & White, R. K. (2004). Design, Characterization, and Evaluation of a Small-Scale Diesel Exhaust Exposure System. Aerosol Science and Technology, 38(1), 62-78. doi:10.1080/02786820490247623Brown, D. M., Wilson, M. R., MacNee, W., Stone, V., & Donaldson, K. (2001). Size-Dependent Proinflammatory Effects of Ultrafine Polystyrene Particles: A Role for Surface Area and Oxidative Stress in the Enhanced Activity of Ultrafines. Toxicology and Applied Pharmacology, 175(3), 191-199. doi:10.1006/taap.2001.9240Lighty, J. S., Veranth, J. M., & Sarofim, A. F. (2000). Combustion Aerosols: Factors Governing Their Size and Composition and Implications to Human Health. Journal of the Air & Waste Management Association, 50(9), 1565-1618. doi:10.1080/10473289.2000.10464197Kittelson, D. B. (1998). Engines and nanoparticles. Journal of Aerosol Science, 29(5-6), 575-588. doi:10.1016/s0021-8502(97)10037-4Dockery, D. W., Pope, C. A., Xu, X., Spengler, J. D., Ware, J. H., Fay, M. E., … Speizer, F. E. (1993). An Association between Air Pollution and Mortality in Six U.S. Cities. New England Journal of Medicine, 329(24), 1753-1759. doi:10.1056/nejm199312093292401Sem, G. J. (2002). Design and performance characteristics of three continuous-flow condensation particle counters: a summary. Atmospheric Research, 62(3-4), 267-294. doi:10.1016/s0169-8095(02)00014-5Ankilov, A., Baklanov, A., Colhoun, M., Enderle, K.-H., Gras, J., Julanov, Y., … Zagaynov, V. (2002). Intercomparison of number concentration measurements by various aerosol particle counters. Atmospheric Research, 62(3-4), 177-207. doi:10.1016/s0169-8095(02)00010-8Wiedensohlet, A., Orsini, D., Covert, D. S., Coffmann, D., Cantrell, W., Havlicek, M., … Litchy, M. (1997). Intercomparison Study of the Size-Dependent Counting Efficiency of 26 Condensation Particle Counters. Aerosol Science and Technology, 27(2), 224-242. doi:10.1080/02786829708965469Giechaskiel, B., Ntziachristos, L., & Samaras, Z. (2004). Calibration and modelling of ejector dilutors for automotive exhaust sampling. Measurement Science and Technology, 15(11), 2199-2206. doi:10.1088/0957-0233/15/11/004Cheng, M.-D., Storey, J. M., Wainman, T., & Dam, T. (2002). Impacts of venturi turbulent mixing on the size distributions of sodium chloride and dioctyl-phthalate aerosols. Journal of Aerosol Science, 33(3), 491-502. doi:10.1016/s0021-8502(01)00180-xHueglin, C., Scherrer, L., & Burtscher, H. (1997). An accurate, continuously adjustable dilution system (1:10 to 1:104) for submicron aerosols. Journal of Aerosol Science, 28(6), 1049-1055. doi:10.1016/s0021-8502(96)00485-5Lyyränen, J., Jokiniemi, J., Kauppinen, E. I., Backman, U., & Vesala, H. (2004). Comparison of Different Dilution Methods for Measuring Diesel Particle Emissions. Aerosol Science and Technology, 38(1), 12-23. doi:10.1080/02786820490247579Wong, C. P., Chan, T. L., & Leung, C. W. (2003). Characterisation of diesel exhaust particle number and size distributions using mini-dilution tunnel and ejector–diluter measurement techniques. Atmospheric Environment, 37(31), 4435-4446. doi:10.1016/s1352-2310(03)00571-5Liu, Z. G., Ford, D. C., Vasys, V. N., Chen, D.-R., & Johnson, T. R. (2007). Influence of Engine Operating Conditions on Diesel Particulate Matter Emissions in Relation to Transient and Steady-State Conditions. Environmental Science & Technology, 41(13), 4593-4599. doi:10.1021/es0616229Liu, Z. G., Vasys, V. N., & Kittelson, D. B. (2007). Nuclei-Mode Particulate Emissions and Their Response to Fuel Sulfur Content and Primary Dilution during Transient Operations of Old and Modern Diesel Engines. Environmental Science & Technology, 41(18), 6479-6483. doi:10.1021/es0629007Desantes, J. M., Bermúdez, V., Pastor, J. V., & Fuentes, E. (2004). Methodology for measuring exhaust aerosol size distributions from heavy duty diesel engines by means of a scanning mobility particle sizer. Measurement Science and Technology, 15(10), 2083-2098. doi:10.1088/0957-0233/15/10/019Lapuerta, M., Armas, O., & Gómez, A. (2003). Diesel Particle Size Distribution Estimation from Digital Image Analysis. Aerosol Science and Technology, 37(4), 369-381. doi:10.1080/02786820300970Wiedensohler, A. (1988). An approximation of the bipolar charge distribution for particles in the submicron size range. Journal of Aerosol Science, 19(3), 387-389. doi:10.1016/0021-8502(88)90278-9Wen, H. Y., Reischl, G. P., & Kasper, G. (1984). Bipolar diffusion charging of fibrous aerosol particles—II. charge and electrical mobility measurements on linear chain aggregates. 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Análisis de series de testaje de ganado retinto mediante redes neuronales artificiales: primeros resultados
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