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

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

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

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

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

Multi-technique characterisation of MOVPE-grown GaAs on Si

The heterogeneous integration of III-V materials on a Si CMOS platform offers tremendous prospects for future high speed and low power logic applications. That said this integration generates immense scientific and technological challenges. In this work multi-technique characterisation is used to investigate properties of GaAs layers grown by Metal-Organic Vapour Phase Epitaxy (MOVPE) on Si substrates - (100) with 4⁰ offset towards - under various growth conditions. This being a crucial first step towards the production of III-V template layers with a relatively lower density of defects for selective epitaxial overgrowth of device quality material. The optical and structural properties of heteroepitaxial GaAs are first investigated by micro-Raman spectroscopy and photoluminescence and reflectance measurements. High-resolution X-ray diffraction (HR-XRD) is used to investigate structural properties. Advanced XRD techniques, including double-axis diffraction and X-ray crystallographic mapping are used to evaluate degrees of relaxation and distribution of the grain orientations in the epilayers, respectively. Results obtained from the different methodologies are compared in an attempt to understand growth kinetics of the materials system. The GaAs overlayer grown with annealing at 735⁰C following As predeposition at 500⁰C shows the best crystallinity. Close inspection confirms the growth of epitaxial GaAs preferentially oriented along (100) embedded in a highly-textured polycrystalline structure

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). 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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. Journal of Aerosol Science, 15(2), 103-122. doi:10.1016/0021-8502(84)90030-2Oh, H., Park, H., & Kim, S. (2004). Effects of Particle Shape on the Unipolar Diffusion Charging of Nonspherical Particles. Aerosol Science and Technology, 38(11), 1045-1053. doi:10.1080/027868290883324Matti Maricq, M. (2007). Chemical characterization of particulate emissions from diesel engines: A review. Journal of Aerosol Science, 38(11), 1079-1118. doi:10.1016/j.jaerosci.2007.08.001Katz, J. L. (1970). Condensation of a Supersaturated Vapor. I. The Homogeneous Nucleation of the n‐Alkanes. The Journal of Chemical Physics, 52(9), 4733-4748. doi:10.1063/1.1673706Burtscher, H. (2005). Physical characterization of particulate emissions from diesel engines: a review. Journal of Aerosol Science, 36(7), 896-932. doi:10.1016/j.jaerosci.2004.12.001Mamakos, A., Ntziachristos, L., & Samaras, Z. (2004). Comparability of particle emission measurements between vehicle testing laboratories: a long way to go. 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