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A further observation on sperm structure in a Heterodera sp.

RESP-873

Response of the northern stratospheric polar vortex to the seasonal alignment of QBO phase transitions

This study considers the strength of the Northern Hemisphere Holton-Tan effect (HTE) in terms of the phase alignment of the quasi-biennial oscillation (QBO) with respect to the annual cycle. Using the ERA-40 Reanalysis, it is found that the early winter (Nov–Dec) and late winter (Feb–Mar) relation between QBO phase and the strength of the stratospheric polar vortex is optimized for subsets of the 44-year record that are chosen on the basis of the seasonality of QBO phase transitions at the 30 hPa level. The timing of phase transitions serves as a proxy for changes in the vertical structure of the QBO over the whole depth of the tropical stratosphere. The statistical significance of the Nov–Dec (Feb–Mar) HTE is greatest when 30 hPa QBO phase transitions occur 9–14 (4–9) months prior to the January of the NH winter in question. This suggests that there exists for both early and late winter a vertical structure of tropical stratospheric winds that is most effective at influencing the interannual variability of the polar vortex, and that an early (late) winter HTE is associated with an early (late) progression of QBO phase towards that structure. It is also shown that the seasonality of QBO phase transitions at 30 hPa varies on a decadal timescale, with transitions during the first half of the calendar year being relatively more common during the first half of the tropical radiosonde wind record. Combining these two results suggests that decadal changes in HTE strength could result from the changing seasonality of QBO phase transitions. Citation: Anstey, J. A., and T. G. Shepherd (2008), Response of the northern stratospheric polar vortex to the seasonal alignment of QBO phase transitions, Geophys. Res. Lett., 35, L22810, doi:10.1029/2008GL035721

Yb:YAG planar waveguide lasers grown by pulsed laser deposition: 70% slope efficiencies at 16 W of output power

We present our recent advances in the use of pulsed laser deposition (PLD) to fabricate active gain elements for use as amplifiers and laser oscillators. Record output powers exceeding 16 W and slope efficiencies of 70% are reported for optimized epitaxial growth of Yb(7.5%):YAG on to YAG substrates. We show for the first time that the performance of PLD material can meet or even exceed that of materials grown by more established methods such as the Czochralski technique. Details of fabrication, characterization and laser performance are presented in addition to outlining expected future improvements

Comparative study of rare-earth doped sesquioxides grown by pulsed laser deposition and their performance as planar waveguide lasers

The sesquioxides yttria, scandia and lutetia have been identified as promising host materials for high power lasers due to their excellent thermal properties, their ability to incorporate RE-ions and their resulting spectroscopic properties [1]. However, the melting points of these materials exceed 2400°C and are therefore problematic to grow from the melt. Pulsed laser deposition (PLD) is an alternative method of growing thin crystalline films of these materials, avoiding the requirement for such high temperature growth

Second-harmonic generation in a direct-bonded periodically-poled-LiNbO₃ buried waveguide

We report the fabrication of a 12µm-thick periodically poled LiNbO3 planar waveguide buried in LiTaO3 by direct bonding of precision-polished surfaces. Frequency doubling of the 1064nm output of a cw diode-pumped Nd:YAG laser was performed in a 5.5mm-long device with a 6.50µm-period grating at an elevated temperature of 174°C. The resultant green second-harmonic output exhibited fundamental-spatial-mode characteristics at a 4.3% /W conversion efficiency

Motivational Social Visualizations for Personalized E-Learning

A large number of educational resources is now available on the Web to support both regular classroom learning and online learning. However, the abundance of available content produces at least two problems: how to help students find the most appropriate resources, and how to engage them into using these resources and benefiting from them. Personalized and social learning have been suggested as potential methods for addressing these problems. Our work presented in this paper attempts to combine the ideas of personalized and social learning. We introduce Progressor + , an innovative Web-based interface that helps students find the most relevant resources in a large collection of self-assessment questions and programming examples. We also present the results of a classroom study of the Progressor +  in an undergraduate class. The data revealed the motivational impact of the personalized social guidance provided by the system in the target context. The interface encouraged students to explore more educational resources and motivated them to do some work ahead of the course schedule. The increase in diversity of explored content resulted in improving students’ problem solving success. A deeper analysis of the social guidance mechanism revealed that it is based on the leading behavior of the strong students, who discovered the most relevant resources and created trails for weaker students to follow. The study results also demonstrate that students were more engaged with the system: they spent more time in working with self-assessment questions and annotated examples, attempted more questions, and achieved higher success rates in answering them

A stochastic model for heart rate fluctuations

Normal human heart rate shows complex fluctuations in time, which is natural, since heart rate is controlled by a large number of different feedback control loops. These unpredictable fluctuations have been shown to display fractal dynamics, long-term correlations, and 1/f noise. These characterizations are statistical and they have been widely studied and used, but much less is known about the detailed time evolution (dynamics) of the heart rate control mechanism. Here we show that a simple one-dimensional Langevin-type stochastic difference equation can accurately model the heart rate fluctuations in a time scale from minutes to hours. The model consists of a deterministic nonlinear part and a stochastic part typical to Gaussian noise, and both parts can be directly determined from the measured heart rate data. Studies of 27 healthy subjects reveal that in most cases the deterministic part has a form typically seen in bistable systems: there are two stable fixed points and one unstable one.Comment: 8 pages in PDF, Revtex style. Added more dat