6,222 research outputs found
Study of the winter 2005 Antarctica polar vortex
During winter and springtime, the flow above Antarctica at high altitude
(upper troposphere and stratosphere) is dominated by the presence of a vortex
centered above the continent. It lasts typically from August to November. This
vortex is characterized by a strong cyclonic jet centered above the polar high.
In a recent study of our group (Hagelin et al., 2008) of four different sites
in the Antarctic internal plateau (South Pole, Dome C, Dome A and Dome F), it
was made the hypothesis that the wind speed strength in the upper atmosphere
should be related to the distance of the site to the center of the Antarctic
polar vortex. This high altitude wind is very important from an astronomical
point of view since it might trigger the onset of the optical turbulence and
strongly affect other optical turbulence parameters. What we are interested in
here is to localize the position of the minimum value of the wind speed at high
altitude in order to confirm the hypothesis of Hagelin et al. (2008).Comment: 3rd ARENA conference, 11-15 May 2009 EAS Publication Serie
PHOTOPERIOD EFFECTS ON 2N POLLEN PRODUCTION, RESPONSE TO ANTHER CULTURE, AND NET PHOTOSYNTHESIS OF A DIPLANDROUS CLONE OF SOLANUM PHUREJA
Flow-cytometric analysis of pollen samples obtained from Solanum phureja, clone PP5, grown under 10, 14, and 18 hour photoperiods at the Southeastern Plant Environment Laboratories of North Carolina State University yielded two populations of pollen based on size parameters. These populations corresponded to pollen separation based on propidium iodide staining of DNA. Anther culture response from plants grown under 14 and 18 hour photo periods for 8, I 0, 12, and 14 weeks was greatest from 8 week old plants grown under a 14 hour photoperiod. Net photosynthesis was significantly higher for plants grown under a 10 hour photoperiod than for plants grown under either a 14, or 18 hour photoperiod. A significant positive correlation was found between net photosynthesis and tuber yield. Results suggest that vegetative growth is increased under short photoperiods, floral development is favored under long photoperiods, and androgenesis is greatest from young plants grown under an intermediate photoperiod
Variability for Critical Photoperiod for Tuberization and Tuber Yield Among Monoploid, Anther-derived Genotypes of Solanum phureja
Monoploid genotypes (2n = x = 12), derived by anther culture of a diplandrous (2n pollen-producing) clone of Solanum phureja Juz. & Buk., a South American diploid potato species, were examined for their use in germplasm development. Nine monoploid genotypes and the anther-donor genotype were grown in three chambers (10-, 14-, and 18-hr daylengths) to examine the effect of photoperiod on tuber yield and to determine the variability for critical photoperiod for tuberization. Significant differences were found among the monoploid genotypes for tuber weight and tuber number. Longer photoperiod treatments decreased and delayed tuberization. Axillary tuber formation from single-node cuttings was used to estimate the onset of tuber induction and demonstrated variability among monoploid genotypes for critical photoperiod for tuberization
PHOTOPERIOD EFFECTS ON 2N POLLEN PRODUCTION, RESPONSE TO ANTHER CULTURE, AND NET PHOTOSYNTHESIS OF A DIPLANDROUS CLONE OF SOLANUM PHUREJA
Flow-cytometric analysis of pollen samples obtained from Solanum phureja, clone PP5, grown under 10, 14, and 18 hour photoperiods at the Southeastern Plant Environment Laboratories of North Carolina State University yielded two populations of pollen based on size parameters. These populations corresponded to pollen separation based on propidium iodide staining of DNA. Anther culture response from plants grown under 14 and 18 hour photo periods for 8, I 0, 12, and 14 weeks was greatest from 8 week old plants grown under a 14 hour photoperiod. Net photosynthesis was significantly higher for plants grown under a 10 hour photoperiod than for plants grown under either a 14, or 18 hour photoperiod. A significant positive correlation was found between net photosynthesis and tuber yield. Results suggest that vegetative growth is increased under short photoperiods, floral development is favored under long photoperiods, and androgenesis is greatest from young plants grown under an intermediate photoperiod
Glass Polymorphism in TIP4P/2005 Water: A Description Based on the Potential Energy Landscape Formalism
The potential energy landscape (PEL) formalism is a statistical mechanical
approach to describe supercooled liquids and glasses. Here we use the PEL
formalism to study the pressure-induced transformations between low-density
amorphous ice (LDA) and high-density amorphous ice (HDA) using computer
simulations of the TIP4P/2005 molecular model of water. We find that the
properties of the PEL sampled by the system during the LDA-HDA transformation
exhibit anomalous behavior. In particular, at conditions where the change in
density during the LDA-HDA transformation is approximately discontinuous,
reminiscent of a first-order phase transition, we find that (i) the inherent
structure (IS) energy, , is a concave function of the volume,
and (ii) the IS pressure, , exhibits a van der Waals-like loop.
In addition, the curvature of the PEL at the IS is anomalous, a non-monotonic
function of . In agreement with previous studies, our work suggests that
conditions (i) and (ii) are necessary (but not sufficient) signatures of the
PEL for the LDA-HDA transformation to be reminiscent of a first-order phase
transition. We also find that one can identify two different regions of the
PEL, one associated to LDA and another to HDA. Our computer simulations are
performed using a wide range of compression/decompression and cooling rates. In
particular, our slowest cooling rate (0.01 K/ns) is within the experimental
rates employed in hyperquenching experiments to produce LDA. Interestingly, the
LDA-HDA transformation pressure that we obtain at K and at different
rates extrapolates remarkably well to the corresponding experimental pressure.Comment: Manuscript and Supplementary Materia
A tale of five fricatives: Consonantal contrast in heritage speakers of Mandarin
This study investigated the production of five Mandarin and English sibilant fricatives by heritage speakers of Mandarin in comparison to native speakers and late learners. Almost all speakers were found to distinguish the Mandarin retroflex and alveolo-palatal, as well as the Mandarin alveolo-palatal and English palato-alveolar. However, fewer distinguished the Mandarin retroflex and English palato-alveolar or the Mandarin and English alveolars, with the majority of heritage speakers falling into this group of "distinguishers" in both cases. These results indicate that heritage speakers, in addition to most late learners, do not have much trouble with the Mandarin post-alveolar contrast, and furthermore, that while native speakers and late learners of Mandarin tend to merge similar Mandarin and English sounds, heritage speakers tend to keep them apart. Thus, of the three groups heritage speakers appear to be the best at maintaining contrast between categories both within and across languages
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