4,962 research outputs found
Few-body decay and recombination in nuclear astrophysics
Three-body continuum problems are investigated for light nuclei of
astrophysical relevance. We focus on three-body decays of resonances or
recombination via resonances or the continuum background. The concepts of
widths, decay mechanisms and dynamic evolution are discussed. We also discuss
results for the triple decay in connection with resonances and
density and temperature dependence rates of recombination into light nuclei
from -particles and neutrons.Comment: 9 pages, 8 figures. Proceedings of the 21st European Few Body
Conference held in Salamanca (Spain) in August-September 201
Direct and sequential radiative three-body reaction rates at low temperatures
We investigate the low-temperature reaction rates for radiative capture
processes of three particles. We compare direct and sequential capture
mechanisms and rates using realistic phenomenological parametrizations of the
corresponding photodissociation cross sections.Energy conservation prohibits
sequential capture for energies smaller than that of the intermediate two-body
structure. A finite width or a finite temperature allows this capture
mechanism. We study generic effects of positions and widths of two- and
three-body resonances for very low temperatures. We focus on nuclear reactions
relevant for astrophysics, and we illustrate with realistic estimates for the
-- and -- radiative capture
processes. The direct capture mechanism leads to reaction rates which for
temperatures smaller than 0.1 GK can be several orders of magnitude larger than
those of the NACRE compilation.Comment: To be published in European Physical Journal
Cytologic Features of Pulmonary Metastasizing Leiomyosarcoma: Report of a Case Diagnosed by Fine Needle Aspiration Cytology
Microtopography and Thickness Measurement with Digital Holographic Microscopy Highlighting and Its Tomographic Capacity
The refocusing capacity is a unique feature of digital holography. In this chapter, we show the capability of reconstructing digital holograms at different planes for different purposes. One of such purposes is to increase the focus depth of the microscope system. First, we show experimental results of the feasibility to perform digital holographic microscopy (DHM) using a Mirau interferometric objective. A profile phase comparison of a 4.2 μm high microlens using interferometry and DHM, extending the depth of focus of the microscope objective as proof of the proposal, is presented. Second, it is also useful in reducing shot noise when using an LED as a light source. In order to attain the reduction noise, we performed an averaging process of phase and amplitude images reconstructed at different reconstruction distances. This reconstruction range is performed within the focus depth of the optical system. We get a reduction of 50% shot noise. Finally, we show a strategy based on this tomographic capability of reducing a ringing effect by using an ideal filter in off‐axis digital holography
Milk production and lamb growth in Ojinegra sheep breed
El presente trabajo pretende caracterizar la capacidad productiva de las ovejas de la raza Ojinegra a dos niveles de condición corporal (CC; BAJA, ≤ 2.50 vs. ALTA, > 2.50) y evaluar el crecimiento de sus corderos para la producción de corderos del tipo lechal (10-12 kg de peso vivo a 45 días de edad máxima). Para el ensayo se utilizaron 58 ovejas Ojinegras de Teruel con parto en invierno. La ración provista fue de 1 kg de pienso al día y paja de cereal a voluntad. Se registró el peso vivo peso (PV) de ovejas y corderos semanalmente durante las seis semanas de lactación, y la CC de las ovejas en el parto, a mitad de lactación (3ª semana) y al destete (6ª semana). De estas ovejas se eligió al azar un grupo de 22 ovejas para llevar a cabo el estudio de la producción de leche y concentraciones de metabolitos en sangre relacionados con el balance energético (ácidos grasos no esterificados, AGNE, y β-hidroxibutirato, BHB). Los resultados mostraron que el PV de la oveja Ojinegra (49,0 ± 1,5 kg) se vio afectado por la semana de lactación (P 0,05). Los contenidos de AGNE y BHB en sangre durante la lactación no se vieron afectados por la CC al parto (p > 0,05), mostrando valores medios de AGNE y BHB de 0,30 ± 0,06 y 0,54 ± 0,02 mmol/l, respectivamente. Sin embargo, los AGNE sí decrecieron significativamente a medida que avanzaba la lactación (P 0,05), obteniéndose una producción media de leche de 813 g/día (producción estándar de 702 ml/día). La ganancia media diaria (GMD) de los corderos durante la lactación fue independiente de la CC de la oveja al parto (148 vs. 154 ± 9 g/día, en ALTA vs. BAJA, P > 0,05). El peso medio de los corderos en el momento del destete fue de 9,6 ± 0,3 kg. De este trabajo se puede concluir que la producción de leche de las ovejas de raza Ojinegra de Teruel es moderada, permitiendo un crecimiento limitado de los corderos que puede condicionar el cumplimiento de la edad máxima para alcanzar el peso de la categoría lechal (45 días hasta 10-12 kg). Estos resultados deberían ser contrastados con futuros estudios que evalúen la capacidad lechera y maternal de dicha oveja con distintos sistemas de manejo y alimentación.The aim of this study was to characterize the productive potential of the Ojinegra sheep breed at two
levels of body condition score (BAJA, ≤ 2.50 vs. ALTA, > 2.50), so that to prospect the production of suckling
lambs (10-12 kg live weight at a threshold of 45 days old). Fifty-eight winter-lambing Ojinegra ewes were used. Ewes were stalled indoors and fed 1 kg of concentrate per day and cereal straw ad libitum.
Live weight (PV) of ewes and lambs were registered weekly during lactation (6 weeks). Body condition
score (CC) of ewes was measured at lambing and at weeks 3 and 6 of lactation. Twenty-two ewes were
randomly selected to evaluate milk production and blood metabolites related with energy balance (nonesterified
fatty acids, AGNE, and β-hydroxybutyrate, BHB). Ewes’ PV after lambing was affected by the
week of lactation (P 0.05). Blood AGNE and BHB contents
were not affected by CC at lambing (P > 0.05), with mean values of 0.30 ± 0.06 and 0.54 ± 0.02 mmol/l
for AGNE and BHB respectively. However, AGNE concentration decreased during lactation (P < 0.001). Week
of lactation and CC at lambing had no effect on milk production (P > 0.05); with mean milk production
of 813 g/day (mean standardized production 702 ml/day). The average daily gain (ADG) of lambs was not
affected by ewes’ CC at lambing (148 vs. 154 ± 9 g/day, for ALTA vs. BAJA, respectively; P > 0.05). The average
PV of lambs at weaning was 9.6 ± 0.3 kg. In conclusion, milk production of Ojinegra sheep breed
is moderate and it might condition the attainment of target 10-12 kg live-weight for suckling lamb category
at a maximum age of 45 days old. These results should be confirmed in future studies, assessing the
maternal capacity of Ojinegra ewe under diverse management and feeding systems
Measurement of radium and thorium isotopes in environmental samples by alpha-spectrometry
The final publication is available at Springer via http://dx.doi.org/10.1007/BF02035979[EN] A new method for the determination of low-level radium and thorium isotopes in environmental samples by α-spectrometry is described. Thorium and radium isotopes were chemically separated from the same sample, by using the same tracer (229Th). Two different ways were explored for the concentration process in water samples, obtaining a chemical yield for Ra isotopes between 70–90% in both cases using KMnO4 as carrier and BaCl2 and FeCl3, respectively. The method can also be directly applied for uranium measurements, but in this case there is a limitation on the range of uranium isotopes that can be analyzed.One of us (M.J.R.A.) is grateful to Institución Valenciana de Estudios e Investigación, Spain (IVEI) for fellowshipRodríguez Álvarez, MJ.; Sánchez, F. (1995). Measurement of radium and thorium isotopes in environmental samples by alpha-spectrometry. Journal of Radioanalytical and Nuclear Chemistry. 191(1):3-13. doi:10.1007/BF02035979S3131911W.H.O. Method of Radiochemical Analysis, Univ. of Tokio, Intern. edition, 23 (1967) 117.T. OKUBO, M. SAKANOUE, Geochem. J., 9 (1975) 221.TJOE-PA LIM, N. K. DAVE, N. R. CLOUTIER, Appl. Radiat. Isot., 40 (1989) 63.G. J. HANCOCK, P. MARTIN, Appl. Radiat. Isot., 42 (1991) 63.M. KOIDE, K. W. BRULAND, Anal. Chim. Acta, 75 (1975) 1.K. J. ODELL, Proc. 4th Symp. on the Determination of Radionuclides in Environmental and Biological Materials, April 1983, Ed-Rd Press, London.L. HALLSTADIUS, Nucl. Instrum. Methods Phys. Res., 223 (1984) 266.Radionuclide Transformations, Annals of the ICRP, ICRP Publication 38, Pergamon Press, Vol. 11, 1983, p. 13.M. J. RODRÍGUEZ-ALVAREZ, F. SÁNCHEZ, E. NAVARRO, Proc. 3rd Inter. Summer School, Huelva Spain, M. GARCÍA-LEÓN and G. MADURGA (Eds), World Scientific, Singapore, 1994.M. J. RODRÍGUEZ-ALVAREZ, F. SÁNCHEZ, J. Radioanal. Nucl. Chem., 190 (1995) 123.C. W. SILL, Anal. Chem., 49 (1977) 618.J. L. GASCÓN MURILLO, PhD Thesis, University of Zaragoza, Spain, 1990.M. C. MORÓN, A. MARTINEZ-AGUIRRE, M. GARCÍA-LEÓN, Intern. Conf. on Environmental Radioactivity in the Mediterranean Area, Barcelona, 10–13 May 1988. SNE-ENS, Barcelona, 1988, p. 111.M. YAMAMOTO, K. KOMURA, K. UENO, Radiochim. Acta, 46 (1989) 137.R. GARCÍA-TENORIO, M. GARCÍA-LEÓN, G. MADURGA, C. PIAZZA, Anal. Física B, 82 (1986) 238
Coherent exciton-vibrational dynamics and energy transfer in conjugated organics
Coherence, signifying concurrent electron-vibrational dynamics in complex natural and man-made systems, is currently a subject of intense study. Understanding this phenomenon is important when designing carrier transport in optoelectronic materials. Here, excited state dynamics simulations reveal a ubiquitous pattern in the evolution of photoexcitations for a broad range of molecular systems. Symmetries of the wavefunctions define a specific form of the non-adiabatic coupling that drives quantum transitions between excited states, leading to a collective asymmetric vibrational excitation coupled to the electronic system. This promotes periodic oscillatory evolution of the wavefunctions, preserving specific phase and amplitude relations across the ensemble of trajectories. The simple model proposed here explains the appearance of coherent exciton-vibrational dynamics due to non-adiabatic transitions, which is universal across multiple molecular systems. The observed relationships between electronic wavefunctions and the resulting functionalities allows us to understand, and potentially manipulate, excited state dynamics and energy transfer in molecular materials.Fil: Nelson, Tammie R.. Los Alamos National Laboratory; Estados UnidosFil: Ondarse Alvarez, Dianelys. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Oldani, Andres Nicolas. Universidad Nacional de Quilmes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rodríguez Hernández, Beatriz. Universidad Nacional de Quilmes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Alfonso Hernandez, Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Galindo, Johan F.. Universidad Nacional de Colombia; ColombiaFil: Kleiman, Valeria D.. University of Florida; Estados UnidosFil: Fernández Alberti, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Roitberg, Adrián. University of Florida; Estados UnidosFil: Tretiak, Sergei. Los Alamos National Laboratory; Estados Unido
Identifying Sources of Information That Students Use in Deciding Which Engineering Major to Pursue
This study explores the sources of information that first year engineering students use to decide which engineering major to pursue for their undergraduate studies. The purposes of this study are twofold: (1) to understand how students make an informed decision of which engineering major to pursue and (2) to help the First Year Engineering (FYE) program administration improve the informational resources they provide the students. This study was framed within the FYE population of a large Midwestern university and was commissioned by the FYE program.
FYE administration conducts regular student surveys for feedback and improvement purposes. We analyzed different survey data collected over a period of one year and found out that students identified “Self-Led Exploration of Engineering Disciplines” (SLE) as the single most important source of information in selecting a major. SLE is a broad, ill-defined term, which students may interpret differently. Hence, we developed a qualitative study to investigate how students perform SLE. We conducted individual interviews with 12 students enrolled in the FYE Program. These students were selected so that they were representative of the entire student population in terms of gender. The qualitative findings of this study reinforce that the students are basing their decision of a major using SLE. These findings also helped us unpack the meaning of SLE, and we further came up with 6 different types of SLE. Finally, our findings also indicated that direct interaction with people was highly valued by the students while selecting a major
Effect of cooling rate during solidification on the hard phases of M23C6-type of cast CoCrMo alloy
Microstructural morphology of CoCrMo alloy by control of the cooling rate during the solidification was investigated. Samples were obtained using both an induction furnace for slow cooling rate and electric arc furnace for fast cooling rate. Microstructural characterizations were performed with metallographic techniques. It was found that the difference between the formation temperature of hard secondary phases of M23C6-type carbides determine the reduction of carbide size by increasing the cooling rate
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