La temperatura y la selección de frutos favorecen la germinación de semillas del árbol tropical Myroxylon balsamum (Fabaceae)

Introduction: Myroxylon balsamum is a tree species native to the Neotropics; and its populations may be declining due to logging and habitat loss. Objective: To evaluate the germinative response of seeds under three temperature conditions, and in fruits selected by seed-chamber thickness. Methods: The fruits were collected in the Central Valley of Costa Rica between November 2019 and June 2020. The germinative response was evaluated at 20ºC, 20/30ºC and 30ºC. The thickness of the seed-chambers was measured and dissected. The fruits were classified as filled (thickness ≥ 0,7cm) and as vain (thickness < 0,7cm). Seed germination within fruits was evaluated at 20ºC, 20/30ºC and 30ºC. Results: As the temperature increased, the time for 50% of the seeds to germinate decreased, and the number of seeds germinated per day, increased. However, there was contamination by pathogens, which caused seed death. Filled fruits germinated well at the three temperatures (92% at 20/30ºC; 86% at 30ºC), while in the vain fruits there was germination only at 20/30ºC (4%) and pathogen contamination could be controlled. Conclusion: The germination for this tree is favored at 20/30ºC and at 30ºC, as long as seeds remain inside fruits with subglobose seed-chambers (thickness ≥ 07cm).Introducción: Myroxylon balsamum es una especie de árbol nativa del neotrópico, cuyas poblaciones podrían estar reduciéndose debido a la tala y a la pérdida de su hábitat. Objetivo: Evaluar la respuesta germinativa de las semillas en tres condiciones de temperatura y en frutos seleccionados según el grosor de la cámara seminífera. Metodología: Los frutos se recolectaron en el Valle Central de Costa Rica entre noviembre de 2019 y junio de 2020. Las semillas se extrajeron y se evaluó la respuesta germinativa a 20ºC, 20/30ºC y 30ºC. Se midió el grosor de las cámaras seminíferas y se diseccionaron. Los frutos se clasificaron en llenos (grosor ≥ 0,7cm) y en vanos (grosor < 0,7cm). Se evaluó la germinación de las semillas dentro de los frutos a 20ºC, 20/30ºC y 30ºC. Resultados: Al incrementarse la temperatura, disminuyó el tiempo para que el 50% de las semillas germinaran y aumentó el número de semillas germinadas por día. Sin embargo, hubo contaminación por patógenos, lo que provocó muerte de semillas. En los frutos llenos, hubo germinación en las tres temperaturas, siendo alta y similar a 20/30ºC (92%) y 30ºC (86%), mientras que en los vanos solo hubo germinación a 20/30ºC (4%). En este caso, la contaminación por patógenos se pudo controlar. Conclusión: La germinación de semillas del árbol de bálsamo se favorece a 20/30ºC y a 30ºC, siempre y cuando permanezcan dentro de frutos que tengan cámaras seminíferas subglobosas (grosor ≥ 0,7cm)

Multiple Front Propagation Into Unstable States

The dynamics of transient patterns formed by front propagation in extended nonequilibrium systems is considered. Under certain circumstances, the state left behind a front propagating into an unstable homogeneous state can be an unstable periodic pattern. It is found by a numerical solution of a model of the Fr\'eedericksz transition in nematic liquid crystals that the mechanism of decay of such periodic unstable states is the propagation of a second front which replaces the unstable pattern by a another unstable periodic state with larger wavelength. The speed of this second front and the periodicity of the new state are analytically calculated with a generalization of the marginal stability formalism suited to the study of front propagation into periodic unstable states. PACS: 47.20.Ky, 03.40.Kf, 47.54.+rComment: 12 page

Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum